https://www.dimensionengineering.com...s/battleswitch
I think you can achieve cutting power to your servos with this switch wired in series with either the signal or black wire coming from the servos to the receiver. You would turn on/off with a 2 position switch on radio.
People use these battle switches to turn on/off lights, I use to use them too to turn on/off hydraulic pump before I had a sophisticated Spektrum computer radio to use ch mixing servos & esc's. I have one lying around that you can have to try, PM your mailing addy & I send it to you Monday.