A too simple answer, he wants to hack the thing.

Basically it is possible as long the design is really a receiver and an ESC in one housing. Problem is tha when merging an ESC and receiver in one housing it possible and done to ditch the channel PWM signals and merge the ESC into the receiver its processor.

You need an oscilloscop and the matching transmitter to follow signals. And if you can fins a PWM signal it is possible to disconnect that from the receiver part and connect it to a different receiver.

But on the other hand, if we are talking about a brushed ESC, you can find one for 10 to 20 bucks.....