Here ya go... Not one of my best CPs, just a little personal thing made out of a wireless Ms. Pac-Man unit. Ignore the white joy, it's just a fusion painted Super. The single white button is menu. The pink block is the Jakks joystick, hot glued in (no real good ways to mount it).
I seem to recall having a discussion bishmasterb, who was going to use a mini wheel on his. I'm not sure what ever happened with it though. I don't think there's any reason you shouldn't be able to do it.
Edit: Looking at the wheel, my only thought is whether or not the thing is strong enough. I've never had problems with the little knob, but the leverage of a wheel might be a different story.