But there is always a way. Do you know much about electronics? You need to wire in a relay between the motor and the control box. You wire it so that the control box doesn't send power to the motor any more, it just sends a little power to the relay to "trip" it (a relay is just a switch that it turned on by electricity – you can get one at Radio Shack).
Say your car runs on 6 volts. You would hook up some batteries with say, 12 volts, and connect one of the wires to the relay, the other wire to the motor, and then run a wire from the relay to the other motor wire. Now, when you press the button on the remote to make it go, the controller in the car will turn on the relay. The relay will connect the 12-volt power to the motor, and off it goes, twice as fast as before.
You might even consider running it at 18 volts. To do this, get 4 or 6 rechargeable 9-volt batteries. Connect them in series pairs – two batteries to make 18 volts, then two more in series, with this series connected in parallel to the first. The more batteries you have in series, the faster it will go. The more you have in parallel, the longer it will run.
Hope this helps!
Rick (engineer)

It’s a great idea for long road trips.