Plyos would be the way to go, as mentioned. You can try loading some weight on a leg press and doing it as fast as possible. It doesn't have to be that much weight, the point is to enable you to exert as much force as possible very quickly, emphasizing the speed. And since you are not lifting that much weight, the muscle would not grow as much. This way you could increase your endurance and speed and keep muscle mass low. At least that's what a coach at my school says...
But my opinion on the whole thing is, yeah, tell your dad to quit it. Tell him that you'd rather weight lift than play soccer. If that fails, I'd give him an ultimatum; either I play soccer and weight lift, or nothing.
-Roek