That's a cheezy way to do a 2 motor mod. The cleanest and nicest looking way is to solder the second motor to the back end of the heat sink. You need to slot and bend it down in the back. This way, you don't even need to run extra positive wire to it. you are already getting it through the sink. It just looks better too.
But listen to me...
I have more power and torque than I know what to do with by just using a single torque'ie motor and 3 cells. (std. ones) All that extra crap is reduculous.
Pay attention here!!! The more motors you add, the more draw you add. With 2 motors and 4 cells, I melted my PCB. 3 motors and 3 cells would SURELY melt it. Too much voltage draw. I can do a 4 cell mod with no problem, but adding motors is what killed my board.