Pardon my lack of understanding (still new), could you do a hard link as appossed to mount --bind ? I believe this should work so long as they're on the same file system (lack of experience here). On the other hand, if they are on different filesystems, you could have the true music dirrectory located at /home/music, do hard links to it, and mount that on top of /var/ftp/music or whatever.
Besides, why are you saying that mounting into the users home dirrectory means you cannot restrict read/write access. Couldn't you have a folder inside their dirrectory that they don't own or have full access to?
Once again, I've bassed this on how I belive the system is set up, not necisarily upon truth. If you tear my post to shreads, then I'll just be happy to have learned better