Stacking motors on the Powered Up hub or Boost hub
All you should have to do is connect pins 1 and 2 between the two motors. One motor will have all six wires connected and serve as the primary in order to give the hub something that it can properly identify. The second motor can simply piggyback off of the primary and share control voltages that are meant for the primary motor. Essentially, you can leave one set of identification circuitry in place, and then wire just the motors in parallel.

I'm not sure if Powered Up compatible connectors are available anywhere, but it's not too hard to open up the motors and connect to them that way. Here's what it looked like testing this out:



I paired pins 1 and 2 here and things worked as expected.