Apparently the elevators aren't so technologically advanced to let someone in charge know when they're malfunctioning. So if you're in desperate need you could probably pull the stop switch for a couple minutes and no one would know.

For further details see the following: http://www.flyertalk.com/forum/showthread.php?t=634625

And if for some reason it doesn't turn back on, you know you have a few hours to bang on the doors.

On a more serious note, I've done the "only step on shoes and don't let the pants touch the floor" routine when changing in bathrooms. Not the best but like jetbluenyfl says, I find that comfort for a few hours is worth the temporary inconvenience of changing in the bathroom. If its really that bad, spread some newspapers on the floor first.