Summer classes without transferring?

I have a question. My son, a junior, still does not have an internship for the summer, and it is starting to look bleak. He had a great idea for a Plan B - he wants to get his M.Acc. after graduating next year, but he is an Economics major and his college only allows non B-school students to take two accounting classes, which he has taken. There are at least 4 more required accounting classes before he can start on his M.Acc., and while some schools have pre-admission programs that allow students to knock them out as part of the Masters program, he thought a good use of time this summer would be to take those classes so he can hit the ground running and also have a good excuse on his resume as to why there is no internship (he had a great one last summer). The problem is this - these courses are not taught at community college as they are upper level. He can’t take them at his current school because he is not a B-school student, so he is wondering if he comes home for the summer whether he can take them at a local state university or even a small private college? Is there a way to do that without officially transferring, or “studying abroad”, which I am sure had deadlines he has missed? If a private school, he would need financial aid and it’s probably too complicated and too late for that. Any suggestions?