Is it possible to enable Legacy FileVault for a network user?
I haven't seen anyone hack together a script to re-implement the FileVault encrypted disk image settings, but I have heard of people using a pre-Mountain Lion machine to make more local users and then migrate them to OS X 10.8.

It requires a second machine (or VM if that is up your alley) but I haven't seen any downsides to moving more FileVault 1 type accounts to new systems other than the obvious downsides associated with those accounts:


backups to Time Machine only run when unlocked
compacting of free space can be problematic
slight slow down and chance of breaking some software that assumes hard coded file paths