Yes. In fact, it's simple in theory and not too fussy in execution.
You will need a tether, at least a 2-wire one. (A 4-wire would allow you to also pick up AC from the track from the dummy and send it forward to your A-unit.)
Disconnect the rev unit in the B, if there is one. Just leave it in place. Locate the wires from the rev unit in the A unit that feed DC to the motors. Add a tether wire to each DC wire out of the rev unit, and do the same thing on the "in" motor wires in the B unit. Connect the tether between the unit and take off.
You are simply adding 2 more motors to the A unit reverser's output. Now - 4 motors instead of 2 will draw more power (amps) from the reversing unit in the A. Monitor the rev unit during use to see if it is getting hot. It probably won't unless you are trying to pull a very large train. Rev units come in different capacities.
It's almost that simple - but get very familiar with your equipment, trace the wires, get comfortable, before you snip or hook-up anything.
