Move mailbox into another user

[maxxer]

Say I have user A which has gone, but I'd like to keep his account into an archive, which is a subfolder in user B.
So A -> B/archive/

Via ZWC I'd mount user A into B and move mailboxes or mails manually... But I'd like to do this via zmprov.
In the past I made some script to move single mails between accounts, but it's pretty slow.
What's the best way to approach this script?

Any suggestion is welcome.
thanks