Your best bet would be to get a toggle switch, rocker switch or a pushbutton-if you check a Radio Shack, they have toggles in all sorts of sizes and shapes, and pushbuttons that will do exactly what you want. They just won't look like an arcade button, but some creative hacking should be able to take care of that. Personally, I just went with a rocker switch, I use it to switch from two player/two joystick (aka Smash TV) configuration to four player: