Actually (2nd reply to this), Reika already knows how to do this, and does it with the CVT and at least one other machine I can think of (where you drop gears in, I forget what its called).Thing is, how do upgrades work with realism.
He requires us to slot in belts and what not to his machines. He's also able to inspect what is in the slot (otherwise I could replace belts with, say, dirt) and drive functionality from that. If he wants.