Yes, you can use a universal speed control on the motor, but you will have to use it on the motor circuit only. A speed control must be designed to operate a motor and not lights. Also, it must be able to handle 5 amps. This is well over the current limits of most speed controls availabe at Wall Mart, so you must order it from a supplier.
A better solution would be to remove the plastic baffle from the drum, this will reduce the stress on the material.