I've never done it, but my uncle did when he was 19 or something, except that he had a series of 3 way switches that had to be in the right positions for the car to start. I'd imagine the only thing you would have to do is find a wiring diagram for the ignition switch, grab one of the wires resposible for stating the car, and splice a button in. I'd be interested to hear from another few people though, just to see if I'm right.