Ya know what I bet that would work. Where would I go to find and X and Y button on a PS2 controller.... Hmmmmmm....
How the hell could've I known that you were talking about a PS2 controller? ):.
On topic: If you're playing with your feet, then there would either be no proof what-so-ever (by record with a VCR), or the quality would be horrible since you'd have to make sure a camera is watching your feet the whole time during the run. Besides, you don't want your controller to smell like feet...
Edit: Oh, and just for the heck of it, there is an X button on a PS2 controller ;p.
Eight years ago I broke my left wrist. For a couple weeks I couldn't exert fine motor control in my left hand without a shooting pain...which led to me playing Super Metroid using one hand and one foot; quite the feat, but I was flexible enough to pull it off. When that got too uncomfortable I could also use one hand by spreading my fingers very wide, particularly when I had to make a jump (thumb on B, index on D-pad).
People can actually beat Mario with their toes, because it's easier.
Back in the day I had a friend who broke his arm, so we tried to figure out what game he could play conveniently with one hand, and we settled on Earthbound. Dragon Warrior 5 or 6 also would have worked. Basically, games with an all-purpose left shoulder button.
People actually make one handed controllers, usually billed as RPG controllers. Here and here are examples. I remember a one handed controller being advertised for the SNES as well. And of course, there's the Revolution.
That second one looks cool I could actually use that since I play a lot of RPGs. And, I doubt anyone will play revolution one handed, I suspect most of the games will need the little add on for the extra analog stick and buttons.
I dunno, I'm a mostly RPG guy myself, but none of those controllers look like they would be very fun to play on. It seems to me that the obvious way to build one would be shaped more like a flight stick. Like, you would have the analog on the front/top, and your other 4 fingers would fit in a natural position around the back and control all the buttons. Kinda like the N64 controller. Mapping squeezing the controller to a turbo feature would be really useful for text advance and other things as well.