Cyrus mailbox (plain files) to Dovecot

Hi,

I'm migrating from a Cyrus to a Dovecot installation right now. As part of it I've got plain Cyrus mailboxes (w/o real metadata; so to say I've got the /var/spool/imap/user part but not the /var/lib/imap/user one)). Those former mailboxes I want to provide under a public namespace via ACLs. The question I cannot answer right now is: How can I convert these plain mailboxes on a FS level to maildir++ so I can provide them as public mailboxes on the new system? The tools I have found require a valid/complete cyrus mailbox. (I don't really care about message flags etc).

Thanks, Wolfgang