Perhaps it isn't as fool-proof as some say it is.

I do have actual physical limitations that prevent me from assuming and holding the position for a clean scan. When I am directed to the NoS (always, I must fit some 'profile') and I explain, I am always told that my limitations make me an 'opt out' and I am sent for a grope. Depending on what I observe, I sometimes wait until I am in the NoS to explain that I can't assume and hold the position. I still get the grope, but I don't have to wait, because oddly enough, there's always a 'resolution' groper standing on the other side of the scanner (not available to grope 'opt outs', apparently).

I have never been just directed to the WTMD instead of the NoS when I explain my limitations. On a very few occasions, I have actually been told I have to demonstrate my limitations for the TSO. I'm not sure why, because I'm still sent off to get hands in my pants and between my legs.