The circuit that dmccormick001 was talking about is located at BIT-Switch www.rc-cam.com/bitsw.htm
Switch Example S1.
To switch the timing or to use in-flight 'Kill' or even turn LEDS on/off use an R/C Switch like we have been talking about. There are lots of different designs that you can make or buy. This one from Pololu is small and cheap. www.pololu.com/catalog/product/1210
Here is a good one if you want to make your own. www.rc-cam.com/bitsw.htm
Here is one that does not require programming but, there is no explaination on how the circuit works. http://www.diyrc.com/aiptekmod.htm
IMHO it seems that the R/C network R1 and C1 will reset U1a after a given amount of time keeping U1b reset until the servo pulse width of the Rx is small enough to set the 'D' pin and clock U2b. This would cause the flip-flop U1b outputs (Q and Qnot) to change state. You can adjust this circuit by changing R1 to a varible resistor.
You can use one of the circuits shown at www.rc-cam.com/bitsw.htm
to ground out the Hall signal or to apply a low or high to any pin. In both cases above you just need 1 open Rx channel for each r/c-switch you want to use.