Seriously though, you cannot change your genetics, and you can't exercise only part of a muscle. You could do isolation curls till the cows come home and it isn't going to train a muscle to change its shape.
For sure, genetics is the big factor. What I'd do is is pull out something like Arnold's Encyclopedia of Modern Bodybuilding or search through that old-school stuff on the theory that it doesn't hurt to try. Something like seated incline DB curls or Arnold-style concentration curls won't work miracles but might provide useful stimulus.