Per OP he doesn’t want anything that could be derogatory of paralyzed people. If the objective is to indicate a situation where action is not possible, why not just use an UP and DOWN arrow side by side, or a LEFT and RIGHT arrow one atop the other?
I think either of garygnu’s links are specific and easily understandable. I can’t see how they could be considered derogatory, and I’m paralyzed 
http://dl.dropbox.com/u/4181904/paralyzed2.gif
Stick figure Charlie Brown and Jesus Christ?
I believe that is the first time in history that sentence has been thought up.