He can get little weights that wrap around the ankles and arms. They attach with buckles or velcro. Using these extra weights during his workout routine will help increase his speed. Once he sheds the weight pads from his body, he'll be able to move faster when he's playing the game.
Of course, there's nothing better than the old adage, Practice Makes Perfect. So, if he adds some resistance during practice, he'll surely notice an improvement in his up coming season - hopefully!