How to reset Keyless Entry code?

I just bought a 2001 Crown Vic LX with the keyless door entry. The manual says to enter the factory code, then go about your business of changing codes, etc.

The dealer did not have the original factory code information (bought from a Toyota dealer that took it in on trade I suppose).

Question: Is there a way, with the key in the ignition or otherwise, to reprogram / reset the code to allow keyless entry via the keypad?

Thanks

Fred