There's no way to set folder level security in the Dashboard, so it will be unsupported. Because Vail manages storage using a different allocation mechanism, it may be possible to set permissions at a lower level than the entire share, but I haven't experimented
with it. If you do so, realize that you may cause problems that can't be fully resolved short of flattening your server...I'm not on the WHS team, I just post a lot. :)