After a fashion, it is possible. On Dreamhost, you can "throttle" bandwidth by "domain", so by tying a domain to a particular user, and a user to a directory, you can have the same effect. It's a slightly different process, but still works.
Like the first answer above, it works a little differently than that, but you can do what you want. DH allows you to set disk storage quota's by user, rather than directories, so you simply tie the user to a given directory, and then limit/raise that user's quota. Since the user can only write to a directory he/she "owns", the net effect is pretty much the same.