you can do a one leg squat on a smith machine, the bar is locked so he is not going to go forward or backward while using it, staright up and down, You can do a one leg seated press, not that hard to do, you can do one leg seated or standing calve raises, You can do one front leg seated extentions, you can do one leg lay down hamstring curls. THINK man THINK!
(no disrespect) but what the hell is the matter some of you asking "how does he work his leg, or call BS on his leg". If your legs aren't growning then maybe you should give up working them, cause obviously you missed the most important part of bodybuilding "switching up your routine to get better results"! It's something this kid learned really quick and has made tremendous progress with it.
Something I believe Kevin Levrone said "a true winner does more and goes further then his competition"..... (or something close to that)