I modified the smoke output on a Williams Challenger years ago and stuck the switch under the cab of the engine to reduce the level of smoke output to half and off. To locate the switch where I wanted it, I think I glued the switch to a piece of pcb material with epoxy. The pcb material was cut so that it could reach an existing screw in the engine. I put a longer screw in its place to accomodate the original screw length plus the thickness of the pcb board. You could also use a thin piece of wood or plastic laminate. In my case you just had to feel under the cab and locate the switch. With a heavy engine there was little chance of derailing it while changing the switch position.
You should have access to the inside of the 2046 or 2055 cab and could mount a switch recessed back inside the cab. Use a black paint pen or sharpie to color the switch and wires black and then even you might not be able to find it. Wherever you locate the switch, remember to allow plenty of room for your finger to get to and move the switch.