get a few $5 gift cards and wrap them in boxes! That is what I would do! Itunes gift cards, EB games gift cards, McDonalds or burger King, what ever he would be likely to use, walmart and target are good too.
Put them in shirt boxes and wrap up...at least it would look like he got a few more gifts!
What about a month pre-paid of a 'net-flix' type thing that does video games?
do they sell t-shirts with his school on it? I know that there are always t-shirts for sale in the school office where my daughter goes for $10...