My kids finally got bored of the hoverboard and I've started tearing it down. I wasn't sure how to control the wheels, there are a few projects where folks use custom firmware. At this point I really don't want a solution that requires that much effort, and even down the road I'll probably just buy a proper ESC.
For now I decided to stick a relay board on the wheel's power lines and leave the current hardware/firmware intact. As long as the pcb is mounted at an angle the hoverboard will always try to send power to the wheels, which I can start/stop with the relays.