I have a 5HP Briggs and Stratton engine. I need a way to turn this thing off on the fly.

Normally I have to take a screwdriver and put it between the spark plug and the steel engine housing to ground out the engine and shut it off.
Would it work to attach some sort of On/Off Switch to the engine? One wire goes to the top of the engine's spark plug ( + ), and one goes to the frame ( - ). That way, instead of jamming a screwdriver in there, I flip on the switch and it grounds the spark plug voltage out to the steel frame.

It sounds sort of logical, but there is one problem. The magneto supposedly produces 10,000 to 20,000 volts of electricity. That is way too much for most switches to suppress I believe. Is there a certain type of high-voltage switch that I can buy?

 

One way I have seen is a piece of metal under one of the head screws that arcs about a 1/2" off the top of the spark plug. you simply push it down against the plug to stop the engine. The metal was about 1/2" wide looked very much like the metal banding used on large crated items.
If you wan to use a switch connect it to the low side of the magneto. This will require removal of the flywheel.