He is coming to the US though on Nov 17th. About the fiance visa - We are getting married in the US next September but then moving to the UK. I thought a fiance visa was only to marry in the US or the UK and then live in the respective country where you were married. So, if that is correct, he cannot get one.
He doesn't have time to get a visitors visa now, I guess he'll just have to tell the truth and we'll hope for the best. I'm going to tell him to take an email between his advisor and him about taking a week off of his master dissertation. It explains why he is going to the US to sort out wedding plans. It seems if he takes that (proof he has school to return to), has a return ticket, and just tells the truth, I don't see any problem.
He didn't seem worried a bit when I talked to him about it. Maybe they've just never given him any problems. 
While you are absolutely correct about being able to marry in the US then leave immediately without a K-1 visa, it is always the prerogative of the immigration officer to say they don't believe you. I'm not in any way trying to scare you, just to make sure you are prepared, which it sounds like you are doing a good job of. You are educating yourself so you can speak intelligently about the processes when questioned, and he will have documentation showing that he has commitments in England and must return. This is exactly what we are having Simon do when he comes next month. He will have letters from his employer, landlord, and others stating that he has commitments there and must return. We can only hope it is enough for immigration, and that they believe him when he says he has no intention of staying illegally.
You see - the whole thing is that they do not want to take the risk of him coming into the country, getting married, then deciding to work out the immigration problems after the fact to stay in the US. Many people try to do this (illegally, I might add), so the immigration officials can be very picky when asking questions. I've also read from members on other immigration sites that they have searched through and read everything in their possession, including private diaries, etc.
So - again - don't be afraid, just be educated and prepared, and above all honest, and you should be fine.
And congrats on your engagement!!!

~Liza