OK, so there's a separate album-centered hierarchical view that organizes Soundtracks, Compilations, etc. Probably not as automated as you're hoping for but it seems to work well as long as you're willing to manually mark the albums as Soundtracks, etc. after you import them. It does clobber the comment field with "Soundtrack" etc. to do this, though, so if you use comments for anything else, it might not be ideal.