I would probably try the following:
>borrow another bike, or some other engine, or temporarily borrow the spark lighter from a gas grill. The idea is to be able to spark the stuck engine's spark plug.
>remove stuck engine's spark plug and clean it if necessary.
>spray in some starting fluid of the ether variety and let some of it evaporate out (some air has to be present in the combustion chamber for the stuff to burn)
>replace spark plug
>connect the spark plug wire from one of the other engines or the spark lighter to your stuck engine's spark plug
>fire the stuck engine's spark plug.
Repeat if necessary. It's not likely to cause damage, but observe reasonable safety precautions.