Yeah, I think at this point the main thing that can be done to raise the score is time. Just keep doing what you're doing, and it will inch up. There's no need to try to boost it more in the short-term; he won't be turned down for credit where he is now.
Someone upthread mentioned opening another cc to make it so your credit limit/credit use ratio gets better; this helps, but it can sometimes be a wash. The average age of all of your credit lines is also a factor in your credit score, and if you have a brand new line of credit (which comes with a credit inquiry, which is also a negative factor), that average age gets dragged down.
Before opening any new lines of credit, to try to improve the credit use ratio, call your current credit card providers and request an increase in your credit limit (even, or perhaps especially, if you have no need for an increased limit). As long as you're paying on time, and not asking too often, they'll often raise the limit a few thousand dollars just because you ask. Voila, you get all the benefits of improving your credit use ratio, without hurting the average age of your credit or incurring an inquiry.