[Dovecot] Compact all maildirs with dovecot-1.0.9?

I'm running dovecot-1.0.9 on Gentoo Linux.

I recently observed a large increase in disk usage on this dedicated mailserver. I attribute it to high spam traffic and/or large attachments for legit email retained on the server.

How can I run a command equivalent to an IMAP client's 'Compact Folder' on the entire tree of maildirs under each /home/(user)?

Thanks.