That's probably the best idea. If you can clearly lay out to him why getting married in the states would be a better option for you and him as a couple, that should help. You don't want your marriage imploding before it's even begun! To be honest, I'm a bit concerned about how his brother (who is VERY anti-American, but likes me anyway) will take it when we make it official, but that's exactly what we're planning to do--explaining to him that it is the cheaper and more practical option. Hopefully he'll agree, but at the end of the day, it's our wedding.
I also don't want to sound negative, but if he's not willing to explain why he's against marriage in the US and instead insists on stomping his foot down and saying "Don't wanna!", then that kind of raises a red flag for me. He should at least listen to what you have to say, and if he still doesn't agree with it, be able to explain why it is that a UK ceremony means so much to him (it'd be a lot easier for you to understand things that way!).
Good luck, keep us posted.