None of the above.
If you're talking about free-throw shooting, then he just needs to practice more and change his stroke and body positioning. If you're talking about field-goals, then he just needs to shoot more, as he's got a great shooting stroke when it comes to field-goals and tres.
He hasn't taken a lot of shots because it hasn't been expected of him and he sees it as a secondary role, but he can shoot the ball, make no mistake ... he had a 55-point game in high school, and went toe-to-toe with Kevin Durant shooting tres in a game of HORSE at the All-Star festivities last year.
If anything, large hands should help a player shoot better, and if anyone thinks he doesn't practice his shot and free-throws, they're sadly mistaken. He just needs to change his style and stroke at the stripe, and make it a more fluid bodily motion.