Verslagen, if it was in gear and the sidestand interlock telling it to shut down, would it still spin?
I Think I know that answer and it's yes, because the second wire from the left, I think, if it gets twelve volts, it spins over even if the key is in your pocket.
The only Safety I can envision would be a switch put in one of the small wires to the start solenoid. That would not be hard.
Remembering to turn it on when you hit the Start button and Nothing happens might be. Finding the Right switch would be a hassle. Hafta be sealed and then installing it for easy access, but the option of having to be on alert like that is a real motivation.
Run a battery dead, cook a starter, ouch..
If the solenoid was arc welded and stuck it would not stop supplying voltage to the starter motor until someone smacked it and shook it loose.
http://www.mooreparts.com/k4-mini-push-button-on-off-triple-sealed-switch-12v...