David, from experience, i would recommend upgrade to V7, it has a utility called FSAUtility which is specifically for moving placeholders. If upgrade is not an option, If i were you i would do some testing. Back up some fileservers including placeholders, restore to alternative location. there is a regisrty key called EnabledVolumes, if you do a search on this site you'll find lots of references to it. Basically its a decimal number that tells EV what volumes are enabled for archiving, you could also run an archive on the volume you've restored to which would create/amend the key.
Good luck, if you need any more help/advice drop me a line
whatever you do, make sure you move the placeholders BEFORE the original server blows up!, Which is what happened to me, which has made the task 100 x more difficult.
Regards
Richard