"Just how big" are these? And just how much (amperage) do you have available in your shop
LOL A slant might be a "little much" (overkill) to drive a compressor. You could use a lot of gas sitting there running.
The basics of "what you'd need" is some sort of governor---You used to be able to find "universal" belt drive governors---and some sort of unloader device compatible with the compressor