A pointer maybe to take a look a what happens when you make a link to a large local disk (called iTunes). The link is done from the "terminal.app" or UNIX prompt, and is in /Users/USERNAME/Music
mv iTunes orig.iTunes
ln -s /Volumes/iTunes iTunes
I use this to link all users to the same Library on the same computer.
Ok /Volumes/iTunes is another locally attached disk, and ok automounter is not employed here. Its not easy to see whats the best way to do this under MacOSX, do I use UNIX or do I use the GUI to do it. Automounter in the generally accepted sense requires a NIS master with all the maps to the filesystems on remote machines, you may not have this.