How can I restore an Exchange 2010 mailbox to its original state after the mailbox has been deleted?

In our environment we are running Exchange 2010 with NetBackup 7 and Symantec eVault. We have global 25 year retention and no purging policies (insane, but that's what the boss wants). We use eVault to simplify and expedite any legal requests for information.

We discovered recently that for several months, July 2013 - October 2013, multiple mailboxes were not being vaulted in eVault - specifically those for exiting employees. Each of these should have an existing vault up to July. We need to restore the mailboxes from backup with NetBackup and then reconnect them to an AD user object and let eVault vault them so that their vault is complete.

Here's where we run into trouble. Ideally, we want to be able to restore each mailbox exactly as it was before it was deleted in Exchange. The purpose being that eVault will then vault the restored mailbox connected with the existing vault, making a single complete vaulted mailbox. But NBU 7 doesn't support granular restore, so we are required to restore an entire database to get to a single mailbox. But that means creating a recovery database for the restore, which means we have to create a new destination mailbox for the recovered mailbox. This means that eVault would create a new vault store for the recovered mailbox which would not be connected to the existing vault for that user. That means 2 mailboxes to search for a single user, should legal require access.

What I would like to do is restore the database, and then connect the mailbox we need to an AD user object, move the mailbox to its original database, and let it get vaulted. Of course, you can't connect mailboxes in a recovery database, nor can you move a disconnected mailbox.

Does anyone know of any way to restore a mailbox to its original state, with original IDs, after the mailbox and AD user have been deleted?

Perhaps someone here knows eVault better than I do and can tell me if it identifies mailboxes/vaults based on the Exchange GUID or AD GUID or SID? If it identifies by AD, then we would have to restore the AD user object as well as the mailbox - and this job is already annoying as we have over 100 users to restore.