When you have it withdrawn, look into whether or not it is better to have it paid out to your son, or you. If it is paid out to him, the earnings portion might be taxed at his rate, not yours, which I assume is lower. Check with your tax professional on this - I'm not completely sure about it. (Even without your specific issue, I have all payouts go to my daughter, and then she repays me anything I have "loaned" to her to cover tuition, etc. up front from the distribution. I have so far avoided getting any letters from the IRS demanding to know why this money wasn't claimed on my return, which some people apparently get when they have the withdrawals go straight to the parents instead of the student or directly to the school. A letter back to the IRS generally resolves the question from what I've read, but I figured I'd rather just avoid that whole back and forth if I could.)
Of course, this only works if you trust him to put the money aside and not spend it on things you don't want him to spend it on. I am still a co-owner on my daughter's credit union account (just haven't bothered to remove it since she turned 18), so when I receive the notification that a distribution was completed, I quickly jump online and transfer anything I am due to my account. Not that I don't trust her to repay me, but she isn't the best at details and could easily spend it without knowing.