I have a design for that but haven't had time to build it. You don't need a speaker, just a motor.Crazy thought: I wonder if anyone has ever used a small guitar mounted speaker to boost that gain/feedback loop, like an extreme version of bringing your guitar close to a speaker to induce more vibration/feedback.
If you could get the physics working OK, find a way to get signal and power to it and control its volume with an expression pedal...instant Santana! LOL.