Just bought a 1999 Limited and learned like most about transponder keys and the B* they are. Found that I only have a Valet key so I can't program new ones. Options are to spend a ton at the dealer or a crap load on a reflashed ECU. Found a free workaround and verified it works. It requires my working Valet key and a non-transponder key.
Followed a video "How to make a cheap transponder key bypass" on YouTube
How to make a cheap transponder key bypass - YouTube (not sure if link will work) with one modification, the relay is not needed. The computer doesn't care if it sees the transponder signal all the time.
I took some thin gauge insulated wire, wrapped it around the antenna ring surrounding the ignition 3 times, using tape and zip ties to secure it. Then wrapped the wire 3 or 4 times around the transponder key and soldered the two ends of the wire together and tucked the key under the dash. Works completely without issue. It basically just sees the valet key signal fulltime. I think this is using near-field magnetic induction but I'm a layman and a tinker so not sure what it's called. I do know it works!
As a note, using a key with an unknown transponder to actually turn the ignition, will confuse the immobilizer and it will start but immediately kill the engine. I cut fresh master keys anticipating that I could program them but couldn't use them since I don't have a programmed master. To salvage them, I cut them open and removed the transponders, then glued them closed again. Both work without issue now. It would also be possible now to probably install a remote start too.
Hope someone finds this and can use it.
Thanks!