For future reference, is there a way or setting I can setup the backup so that when I restore a mailbox it doesn't have to load the complete information store?
Sorry, not at this time. If your BKF files were on disk, you could do direct single item restores
I think that direct single item restores from tape has been posted to the ideas section of the forum (top menu bar, far right). I'm pretty sure that this is a technical problem, tho, not just a design choice