The only thing that will kill your glow engine, other than a blown plug, is a loss of fuel or air supply. Nothing else, An electrical switch will not do squat unless it stops the fuel supply or plugs the air intake in the carb.
If' you've got brakes attached to your throttle, that might not be a great situation. What if you want to reduce throttle and simultaneously applying brakes would be disadvantageous? Could cause a skid, rollover or any number of things in the wrong circumstances. Can't think of any logical reason why brakes should always be coupled to low throttle.
So we're back to the same place. Use your throttle servo to shut the carb. No air = dead engine. To ensure this, the carb must be completely closed. If you still need brakes, why not set things up so that they engage at that point?
Are your brakes acuated mechanically or electrically?
BTW, the old free flight models ran on a specific amount of fuel so that they would quit when it was consumed or had a mechanical timer which cut the fuel supply. Looked like a glorified mousetrap mounted on the side of the fuselage behind the engine with a clockwork wheel and arm around which the fuel line was connected. Dethermalizers were something else, They operated with a fuse and caused the empanage to lift at the rear to terminate a flight.
A photo is worth at least a million words. Have a look here and you'll see what these things are:
http://www.freeflightsupplies.co.uk/timers.htm