Turn a USB mouse into a SNES mouse

[Vertigo]

Seeing this thread made me wonder if it's (easily) possible to throw together your own SNES mouse from a standard USB mouse.
I used to have a SNES mouse but not any more and frankly they're a bit clunky and annoying, so use of a good 2-button LED mouse would make playing SNES mouse games a bit nicer.
How might one go about it?
Does anyone know if it's the same standard 4021 chip inside a SNES mouse? How is it connected/read?
Anyone fancy opening theirs up and doing some hi-res photos?
Thanks.