Trap options just cause problems later on, when the player notices his one trick pony sucks and he's not having fun.
If a player isn't having fun, let him make a new one. It really isn't as difficult as you're making it out to be. You could also try and set up some challenges that let them use their one trick which would, probably, increase their enjoyment of the game. Declining someone's character because you don't like it? I'm glad that I don't have you as a GM. My players can make whatever character they want and even players who make one trick ponies tend to have fun. In the rare instance that someone isn't having fun with their character or they are really just tired of their character, I let them make a new one.