Who'd teach it? Would you teach yourself, or would you be able to take lessons? I would caution against teaching yourself an essay-based subject, because it's not like maths or a science where what you need to know is precisely prescribed and it's easy to see how to answer the questions.
But if you can get access to an expert, then I'd recommend politics, which seems quite interesting, and relevant to the law, tangentially. If you have good background knowledge you might find that that compensates for your lack of time. Personally, I think it's pointless to worry about the 'reputations' of different subjects: they're all ASes after all. With that in mind, I hear Sociology's pretty fulfilling. I would caution you off History, though, because, my course at least, is a lot of work. You should be able to find courses with no coursework in any subject.