[dcb]

The bike thing works, just kinda noisy (magnetic reed switch).

junkyard/autozone hall sensor (vss or crank position sensors), near a magnet strapped on the transmission output hub (with something on the opposite side for balance) would make the basis for a solid vss signal, though I wouldn't run it constantly even with the key removed.

A a kill switch is the typical way of dealing with issues relating to turning the key back. If the kill switch is a well positioned microswitch mounted on the stick shift then it becomes a very "natural" part of your driving style.