buy a regular switch like your RX switch and plug the ignition battery into the female switch and on the male end plug that into the ignition plug. I purchased a Oppto Kill switch that plugs in between the switch and one end plugs into the RX and is turned off and on with the retract (or two way switch on my radio) so its I have to kill the switch in a hurry, I can do it with my throttle cut switch on my TX. Hope this gives you some idea on a direction to go.
NEDYOB