I was a bridesmaid 6 months pg, and had to wear a strapless, backless dress. Those stick on bras didn't come big enough, so we had to create a cantilever system with toupe tape. It looked fab (well, dp certainly thought so, and the brides Mum looked pissed off, so must have been effective). There was another bridesmaid who was small enough for the stick ons - hers ended up looking like little torpedoes!
But they all stayed in place (hers and mine), did their job magnificently, and hurt like hell to get off.