Since this is the System Reserved volume the partition can't be hidden (must be active to boot windows)
After looking at ways to remove the drive letter I think I will abandon using the FDSZ switch and just live with the duplicate IDs.
They are only a problem when techs have to pull the drives from users machines that ID has to be reset (which causes the system not to boot) but since when they usually do this it because the system is un-bootable anyway.
The methods for removing the drive letter don't always have consistancy (i.e. not all disks are disk-0 due to other drives/memory card readers, etc...)
I'll consider this problem solved for now.