it helps if you put the heel of your forward foot on your crank arm and the edge of your BB cluster. that way you can balance by lifting or dropping the toes of your forward foot. then either tuck your back foot behind you (hand on your front wheel) or put it on your wheel to keep your balance. you're well on your way to TOTALLY pissing off everyone who hates hipsters.
i really don't recommend doing this unless you really trust your bottom bracket to not get ****ed up. if you get to the point where you've got one foot on the pedal, the other on the front wheel and no hands on the bars, all of your weight is basically on the top of your crank arm. i have no proof that this is really detrimental, but i believe its a strong possibility.
while this stunt might get you some rounds of applause, possibly a free beer, or a slight chance at some make outs, i guarantee you no one is gonna check your bottom bracket for grindy noises when you go to start riding again.
good luck! ...i guess!