This is not technically an answer...
I recommend creating all virtual machines in /Users/Shared and then applying permissions to the individual folders (i.e. the individual VMs). This has several advantages:
VMs don't take up room in the home directory.
/Users/Shared can be excluded from Time Machine since VMs shouldn't be backed up using Time Machine anyway.
VMs can easily be shared between users on the same Mac. Just create a group for VM users and change the group of the VMs to that group to assign permissions.
It's a clean solution.
Better yet, use a second hard disk for VMs if you can.
I have three VMs (Vista 64, XP 32, SuSE Linux 64) and they are all located on the second internal hard disk which isn't being backed up by Time Machine either.