hehehe
Well, my layout sits on an 30"x80" hollow core door. On top of that, I have a single sheet of 1/2" blue foam (with additional pieces on top of that). When I need to work on my wiring, I simply remove the screws that fasten the foam to the door, then lift the foam up onto 2x2s, and tilt the entire layout back as needed. All of the wires run between the foam and the door (spaced so as to avoid "clumps" that would make the foam noticeably uneven.
(One advantage to this arrangement is that, when the fastening screws are in place, I can lift the door off its legs and move it about without having to worry about snagging any of the wires. The door sits on a pair of TV dinner trays.)
I will be building an HO-scale layout around the perimeter of my son's room, and I've been thinking about using this method to conceal the wires. That way I don't have to worry about making the underside of the shelf "look pretty."
-Rory