Slot car racing - controlling the cars wirelessly

Guys, I and my two boys have a Tomy AFX slot car racing system that we set up and play. We have a load of track so we can set up a long, winding track. The downside though, is that as the speed controllers are connected by a wire, when one of the cars comes off, you have to go over to put it back on the track and one of two things happen; 1) you have to drop the controller, go over to the point where the car comes off, then run back (Me) or 2) run over to where the car has come off, forgetting that the controler is still connected to the track and pull the track apart (the boys)

If there was a way of making the controllers wireless, it would be brilliant. It would mean you could stand where you want and not have to waste as much time when recovering your car.

As i see it, I would need four independent transmitters, of one channel each. That's about the limit of my knowledge of the wireless bit!

The cars get about 22 volts, although clearly the current is not massive. The current controllers are basically a rheastat with a trigger connected to the wiper that contacts the coiled resistive wire.

Any of you clever guys out there know of a relativeley cheap and simple way of making this wireless?