Ooh, what a great idea! I just added you on facebook.
And hey, if you're looking for inspiration, check out my youtube channel. There are a couple of videos in there right now that I think might be what you are trying to do. Here's an example of BTMR done with an improvised soundtrack. It's not really synchronized with the ride at all, but I think it got the right feeling across as an added layer to the ride. Check it out:
[ame=http://www.youtube.com/watch?v=l6jBGi0xcj0&feature=channel_page&fmt=18]YouTube - Big Thunder Mountain Railroad (Full Attraction Experience)[/ame]