fstab.hd is a dummy file. The fact that fstab.hd still exists may mean that you could create a /private/etc/fstab file with the proper syntax and it will would work. I have no idea how tie fstab with open directory but open directory is more or less synonymous with Directory Services or NetInfo in earlier releases of OS X.
So where does Mountain Lion control the mounting of disks?
Via AutoFS. The fstab file is considered legacy technology, but it may be what you need in this case. I have used it to prevent a certain drive from being automatically mounted. You should be able to use it to change the mount point.
Ok, so I founf the answer to my question. Essentially I followed this process;
1) Obtain diskuid from diskutil
3) execute vifs (a program to edit /etc/fstab (/etc/private/fstab)
4) enter the following:
UUID=5A7706F3-4AB4-312D-81FA-A856251663C1 /Users hfs auto
5) Save file
6) Copy /Users content new disk
Sorry for the confusion.