If I'm not mistaken, I think he'll be attending the same university when he gets a diploma?
If that's the case, it's pretty clear he won't have any problems in that regard. He's probably already working towards a degree and will be able to finish in the normal amount of time minus the time he's already been there.
Even if not, your dilemma isn't generally the case. Quite a few people have problems transferring credits, but only when they're upper-divisional courses. All of the dual-enrolment courses I took in high school transfered over when I came to university and waived quite a few classes that I would've had to otherwise take. These include the stupid intro math courses, composition, and chemistry. It saved me about a whole semester's worth of classes.