As zoltanb siad, you just need to answer the personal info questions so that he is not traeted as "can be" claimed as a dependent.
But that may be academic. He is not eligible for the American Opportunity credit because 1. you already claimed it 4 times (the max allowed) on his education and 2. Grad students are not eligible.
He is eligible for the Lifetime Learning Credit (LLC), but that is not refundable. It can only be used as a credit against an actual tax liability. With only $7900 of income, he has no tax liability.
It would actually be better if he was your dependent. You would get a $2000 LLC plus a $500 Other dependent credit.
