There's this website UCCP Open Access
and it looks like a great place where you could study an AP class over the summer. I don't know how you would register and I don't know if there's any teacher, so you might be on your own. However they might not offer the AP class you're looking for so it might depend on which AP class that you're interested in taking. They offer AP Biology, AP Calculus (AB & BC), AP Physics (B & C), AP Environmental Science, AP US History and AP US Government and Politics. Instead of taking an online course I'm just going to go through some prep books this summer to self-study AP Comparative Gov & Human Geography. I think it would be reasonable to study up to two AP classes over the summer. You should enjoy you're summer.
Hope that helps. =]