Saw this setup at the HPI Challenge, & thought some guys might find this useful.. Once installed, it basically acts as a push button that stops your flywheel from spinning, and shuts your engine down. I wouldn't suggest it for racers, as it could be a problem when turn marshalls try to flip your truck on the track...
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXJYM1&P=7
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXJYM1&P=7