campbell that sounds like an interesting idea. gonna try it.
one thing you might want to consider, if you feel like doing a custom jobby, is to study the brake setup on most sachs bikes... theyve got the "pedal backwards" rear brakes that will lock up the rear wheel in no time. im not sure exactly how their setup works, i believe it incorporates some kind of claw clutch, because you can still pedal forwards but not backwards.
i plan on doing this, but not necessarily using the claw clutch idea. a little over complicated. Im thinking instead of just getting some good fat motorcycle brake cable, and rigging up something on my moby so that pedaling backwards will pull the cable. shouldn't be too difficult, i dont think, although i will probably loose fullrotation of my pedals (not that i care, cause i push start and dont have a pedal chain anyways).
this probably isnt the idea youre looking for though. just saying that you can always crank out a lot more power with your legs than your hands.