you could just be bondish and buy this relay that opens and closes when you swipe a magnet over it. just have it between the start switch and your power. you get in the car, swipe your magnet over your hidden relay and push a button. i would try and put a magnet in a ring or a pen, something like that....but i sort of weird, might not be what your looking for.
if you want i can try and find the original link where i read about it.