Actually here in the states the AMA has trouble with this.... says that all control needs to be through the wires... that said there is a basement industry of guys that take an RC transmitter apart and rewire it (like a servo driver) to send a signal down the lines to control the model. It has been used in Scale for maybe 10 or 15 years. They do not use it for elevator control as direct input from a normal handle is much more precise and actually much more powerful than any servo other than some used in quarter scale models. (think hanging a 7 pound scale model on one line giving full up control...)
Bob Furr