per-directory quotas possible on 5.x ?

[Josh Brooks]

Normally, quotas work on a per-user, per-filesystem basis - so if a user
has a home directory and other processes _not owned by that user_ are
placing files and using up space into that directory, it will not count
toward the quota (unless they get chowned/chgrpd to that user/group).

Is there any way to enforce a quota on a directory, regardless of what
ownership or group ownership the files and dirs inside the directory -
that is to say, take directory X, located at an arbitrary spot on the
system, I want it to grow no larger than size Y.

I know this can be done by creating a lot of little partitions - maybe
even vn-backed parttion-on-file, but that seems like a hack, as they would
be hard to resize.

I am looking for a way to force a changeable quota on a directory,
regardless of what gets put in it, or who owns what gets put in it.

Any hacks/asuggestions/comments of any kind are very appreciated.