Never seen that done before, most people want to do it the other way around :-)
It's only a matter of serial protocol conversion, you'd probably just need to write a bit of PIC assembly code to do it.
Contact Guido Mersmann geitNOSPAM@gmx.de (remove NOSPAM)
He's very clever and has done a lot with Amiga keyboard protocols, might have done something like that already.
If you buy him some beers, he might even write the software for you?? :pint: