I fitted a steel wire with T-extension under one of the the diaphragm cover screws. The T could push on the diaphragm through the central cover hole. When pushed down, the carb pump pressure will go directly to the jets, and squirts a generous amount of fuel in the carb bore for choking, or engine stopping.
Be sure it will not touch the diaphragm boss when at rest. Leave at least 1mm space so the diaphragm is free to do what it has to do.