I don't know; you can't really motivate someone to take a talent to the next level if it's not something they may want. For him, he may be terrifically talented but music may just be something very personal. Maybe he just likes entertaining his friends/family. I would just continue to express how much you like what he does and ask him point-blank if he intends to do anything with it. You might be surprised by the answer.
[FONT=Tahoma]"All I can do is be me ... whoever that is". Bob Dylan [/FONT]