i haven't yet worked out to add things like this to the docks, but, you could always add the shared folder as a desktop mounted folder.
WGM>select user group/preferences/login/items/'always' manage/add share points
if you connect to the shared folder on your admin mac and mount the share on your desktop you can drag this point into the 'item' panel. make sure you also select the afp mount point you've added and tick 'mount share point with user's name and password'
hope this helps a little