Many good ideas here in the thread.
But how about using simple bit-bang routines. This will make any old port pin a serial tx or rx.

Plenty of sources available in assembler or c.
Checkout Dave Dunfield's site (www.DDS.com) or Paul Stoffregen's site. I guess at KEIL's (www.keil.com)site there is also some code available.
Snoop around.
If nothing else helps, drop me a note
and I'll send you some files with the neccesary code.

Good luck
Jan