It's already on the loop by the entrance/exit of Hogsmeade, and it'd make more sense on the train ride anyway - it's the easiest choice for music in my opinion.
On that note, I'm really curious as to what they'll do with the story on the way back to London. On the way to Hogwarts it's easy enough to guess it'll include dementor visits and the twins and other magical happenings, but I'm curious as to what they're going to include on the other leg...