From what I read you can program a blank key yourself without any others.
"An alternate programming method is possible and is intended to keep a customer who has no access to a service shop equipped with diagnostic tools from being stranded. This interactive procedure takes approximately 45 minutes to complete to maintain the high level of theft protection provided by the system. When initializing the system using this procedure, it must be followed precisely or the system will abort and the procedure will need to be started over.
Insert an unprogrammed encoded key into the ignition lock and turn ignition switch to RUN. The THEFT indicator will begin flashing.
Follow this procedure three times: After 15 minutes of flashing, the THEFT indicator will extinguish. Within five minutes after the THEFT indicator has gone out, turn the ignition switch once to OFF for a second, then back to RUN. The THEFT indicator will resume flashing for another 15 minutes.
After the third time (at 45 minutes from start), the control module will erase all stored keys and memorize the unprogrammed key as valid. This key will now start the vehicle. Additional keys can be programmed using the Spare Key Programming procedure. "
"The system has capacity to store a maximum of 16 keys. After the initial key has been programmed or using any programmed key, follow the steps below:
NOTE: Encoded keys must have correct mechanical key cut for vehicle.
Cycle ignition switch from RUN to OFF with a programmed key.
Within 15 seconds after this cycle, insert a new encoded key into ignition switch and turn to RUN or START.
If programming is successful, the THEFT Indicator will illuminate for two seconds and the control module will enable the vehicle to start.
Repeat until all chosen keys have been programmed, up to 16 keys total.
If programming is not successful, the THEFT Indicator will:
Flash for one minute if no key code is received. The key is either damaged or is a non-encoded key. (Try a new key and start procedure over again.)
Flash for 15 minutes if key code is received yet vehicle is disabled. The key was not programmed successfully. Start procedure over again.
If programming is not successful, possibly the new key was not inserted within 15 seconds, all 16 key codes have been stored, or the key is a non-encoded key. If the key was not encoded or inserted within 15 seconds, repeat procedure?"
Looks like the +'98s need the dealer and the two already programmed keys.
Key Programming-Erase All Key Codes and Program Two Keys
NOTE: This procedure is when a customer needs keys programmed into the system and does not have two programmed ignition keys available. This procedure is also useful when programmed ignition key(s) have been lost or/and the ignition switch assembly has been replaced, and it is desired to erase key(s) from passive anti-theft system (PATS) memory.
NOTE: This procedure will erase all programmed ignition keys from the vehicle memory and the vehicle will not start until two keys have been reprogrammed to the vehicle. If only one encoded key is supplied to the dealership, a second encoded ignition key must be mechanically cut for the vehicle and programmed. A customer must be notified that other encoded ignition keys in their possession will no longer start the vehicle unless these keys are reprogrammed to the vehicle.
NOTE: Two PATS encoded keys with the correct mechanical cut must be available to perform this procedure. One or both of them may be the customer's original keys.
NOTE: If additional keys are to be programmed, follow Key Programming — Program a Key Using Two Programmed Keys. If the remaining keys are with the customer and are not available with the vehicle, then instruct the customer to refer to the Owner's Manual under the "Programming Spare [SecuriLock (North America) Safeguard (U.K.) or PATS for all other markets.] Keys Procedure" for instructions on programming the remaining keys.
Turn the ignition switch from OFF to RUN.
Enter New Generation STAR Tester Configuration Function Card (NGS/SBDS). Follow the Security Access Procedure to obtain security access.
NOTE: Do NOT select any additional commands from this menu.
From NGS/SBDS menu: Select IGNITION KEY CODE ERASE.
Turn the ignition switch to OFF and disconnect NGS.
Insert the first encoded key into the ignition lock cylinder and turn the switch to RUN for three seconds.
Insert the second encoded key into the ignition lock cylinder and turn the switch to RUN for three seconds.
Vehicle should now start with both ignition keys.
Key Programming-Program a Key Using Two Programmed Keys
NOTE: This procedure only works if two or more programmed ignition keys are available and it is desired to program additional key(s). If two keys are not available, follow Key Programming — Erase All Key Codes and Program Two Keys.
NOTE: PID SPARE_KY must be enabled for this procedure to operate. If this PID is not enabled, then follow the Security Access Procedure above, then select Spare Key Programming Switch: Enabled.
NOTE: If the programming procedure is successful, the new key(s) will start the vehicle and the THEFT INDICATOR will illuminate for approximately 3 seconds.
NOTE: If the programming procedure is not successful, the new key(s) will not start the vehicle and the THEFT INDICATOR will flash. If the programming procedure was not successful, repeat the Key Programming procedure from Step 1. If the failure repeats, check circuit 1001 (W/Y) (hot at all times) in PATS module for proper battery voltage. Repair circuit if voltage is not present. Refer to Diagnosis and Testing to review DTCs and perform Pinpoint Tests as required.
NOTE: A maximum of 8 ignition keys can be programmed to a passive anti-theft system (PATS) equipped vehicle. Use PID NUMKEYS to determine how many keys are programmed to vehicle.
NOTE: If the steps are not performed as outlined, the programming procedure will end.
NOTE: Ignition keys must have correct mechanical key cut for the vehicle and must be a PATS encoded key.
Insert first programmed ignition key into ignition lock cylinder and turn ignition switch from OFF to RUN (maintain ignition switch in RUN for 1 second.
Turn ignition switch to OFF and remove first key from ignition lock cylinder.
Within 5 seconds of turning the ignition switch to OFF, insert the second programmed ignition key into the ignition lock cylinder and turn the ignition switch from OFF to RUN (maintain ignition switch in RUN for 1 second).
Turn ignition switch to OFF and remove second key from ignition lock cylinder.
Within 10 seconds of turning the ignition lock cylinder to OFF, insert the unprogrammed ignition key (new key) into the ignition lock cylinder and turn the ignition switch from OFF to RUN (maintain ignition switch in RUN for 1 second).
If it is desired to program additional key(s), repeat the Key Programming Procedure from the beginning.
Key Programming-Spare Key Programming Switch
NOTE: The Spare Key Programming Switch is a New Generation STAR Tester (NGS/SBDS) programmable switch which provides the capability to enable/disable the normal customer Spare Key Programming Procedure. This procedure is in the Owner's Manual Spare Key Programming Procedure or in this section under Key Programming — Program a Key Using Two Programmed Keys. This programmable switch is provided as a convenience for rental company fleets or other fleet purchasers who may not want the Spare Key Programming procedure available to the vehicle driver.
NOTE: The spare key programming switch state can be viewed by PATS PID SPARE_KY.
Insert a programmed ignition key into the ignition lock cylinder and turn ignition switch from OFF to RUN.
Enter new configuration function card/SBDS. Follow the Security Access Procedure to obtain security access.
NOTE: The default setting on delivery of all new vehicles is <ENABLE>.
From NGS/SBDS menu: Select SPARE KEY PROGRAMMING SWITCH to desired setting:
<ENABLE> Spare Key Programming Procedure is accessible.
<DISABLE> Spare Key Programming Procedure is not accessible.