I know this topic is old, but I wish to bump it, as I was going to request the same thing.
It would be nice if I could create sub-user ftp accounts that can only upload to a certain directory (e.g. media/guynumberone/), as I want to host a shoutcast that me and my friends can all upload music to.
However, I'm obviously a little reluctant to give out the admin account information just so they can have ftp access.
If anybody knows how to manually add ftp users to the passwd file in the meantime, please let me know, it'd be super helpful