Take a look at the savage derringer quick draw. It uses the inertia from the release of the bowstring to free a spring loaded launcher arm held in place by a magnet. Launcher is dropped prior to fletching passing by, especially at the speeds you' re talking. As an added benefit, it just looks and mounts like a normal 2 prong type rest.

I' ve had one on my hunting bow for 2 years now, have never had a problem with it.