Often if I hear that an owner plans to place a picture over a panel to hide it, I will accomadate it by moving cables off center, and put some 3/4" ply above so the hanger can be in something solid, and put the hanger there myself. I would rather do it myself than have the homeowner do it. No one wants to see our work, and I'm happy to accomadate it. I just see it as another part of a good custom install. I would rather be involve in the proccess, than have someone do something dangerous, or create a hazard for me or someone else to work on in the future. And thats for interior sub-panels in residential. Commercial, most of my panels get a room to themselves. And very rarely is a main panel in any place where someone might want to hide it, although I am kind of sick of people planting trees and bushes in front of them. Another situation where I would rather help you hide it than have to fight though a bush to work on it later.

Mark Heller
"Well - I oughta....." -Jackie Gleason