Migrating existing mailboxes to cyrus imapd

[Sherpya]

I must migrate existing unix mailboxes (e.g. /var/spool/mail/bill)
to a cyrus imapd server. I have access to the filesystem (I'm root)
but I don't known user's passwords.
What is the right procedure? (User creation is not a problem, my problem
is moving the emails)
Thx
Sherpya