Buy yourself a 555 timer chip kit and use it switch/interupt the white (signal) wire going from the receiver to the esc, this would cut the signal input to the esc but leave the receiver powered and the steering servo active.
Add a push to make switch you press to start the thing off again.
read this;
http://en.wikipedia.org/wiki/555_timer_IC
for £8 you can buy a circuit kit that uses one
http://www.maplin.co.uk/universal-timer-kit-3315
If you are nervous about switching the signal input then just use this to interupt power instead.
Built one of these when i was 11 years old simple and functional.