I've never had a LC remote opened up so I'm not totally sure what's going on inside, but the human interaction components consist of the three momentary push switches for the sound features and the potentiometer(?) for the speed and direction. If you're going as far as to modify the remote to accept an external power source, could you simply gut the remote, mount the electronic components within signal range of the trains and then run wires to more robust buttons and potentiometers on a more traditional control panel?
Edit: I remembered that I do in fact have a spare remote laying around so I opened it up to see how it was built. All of the switches and the potentiometer are directly soldered to the circuit board vs having wire leads running to them. There is a pair of wire leads running to the battery terminals. The decorative knob seems to be glued to the potentiometer spindle so I wasn't able to remove the circuit board from the front face of the remote as I wanted to keep it intact. I don't see why you couldn't get it apart if you wanted to, but the decorative knob would likely be damaged in the process. It would be easy to solder lead wires to the terminals where the existing momentary pushbutton switches are soldered into the circuit board. The back of the solder pads for the potentiometer are also visible, although in a much tighter grouping than the other terminals. I'm not an electronics guru by any means so I have no idea if it'd be feasible to solder in an external potentiometer in place of the original.
