Guy did it with an Atari mouse here, but in his case it was pretty much a gut one and stuff it full of another mouse. Not sure how you'd do it if one wanted to use the original Amiga connector vs. some sort of adapter. Don't imagine it'd be hard to do if you swapped the guts of an old optical PS2 mouse into the Amiga one and used something like the Micromys adapter, or use a PS2/USB adapter with it in conjunction.
http://geekhack.org/index.php?topic=26542.0
