I seem to recall that we have been repeatedly told that such merging is not possible. However, administrators can do something to correct the splitting, or at least so I understand.
Sorry, there isn't a way to merge accounts yet. The three old accounts "broke" about two years ago. If we were alerted at the time I could have reset them before he posted more messages. He would still have the ghost accounts, but without content. But it is too late now to do that.
I am going back to Jive, though, to see if they might have come up with a way to merge the accounts. No promises, as I have no idea if they can. But it is something we talked about before the ghost account bug was fixed.