The controls in an RC transmitter are simply potentiometers, moved by the joystick. This gives fully proportional control, rather than switched positions - unfortunately it does require a high degree of handling precision. You could replace them with simple switched resistors, where forward is one value, off is another, and reverse is yet another.
A great deal depends on what the RC is required to operate, most RC models need proportional control, so presumably you have something else in mind?.