RE: extension instead of switch?
On my largest sailplane, I mounted a 1/4" stereo jack inline with the RX power supply, such that when the jack is inserted the connection is broken and the RX is dead. The jack has a 12" long red banner hanging from it, so I know if the banner is hanging from my plane, the radio is disconnected.
I once made the mistake of hand-launching a smaller (8') sailplane one day, when I had forgotten to SWITCH my receiver on, and had to hike over 1/4 mile thru the brush and tumbleweeds to get to where it landed, nearly unscathed. I had launched into a ridge of lift, but the feeling of helpless frustration when the model hit a small thermal less than 50 feet from the launch was intolerable!