If you have a decent radio and digital throttle servo, disable the sub trim and set the idle through the radio's program and dedicate a switch to close the idle even further for the engine to stop.

If you don't have a decent radio and servo, simply use the sub trim. Program it so that when it's somewhere in the middle, the engine idles. Just like the nitro engines setup.

I would still recommend using an opto kill switch down the road once the engine is tuned. I program my radio so that if I turn the ignition off, throttle is set to zero also. Failsafe = throttle zero, choke on (I always use a choke servo), ignition off, few degrees right or left rudder.