[Dovecot] disable lazy_expunge for some mailboxes?

How to disable lazy_expunge for certain mailboxes?

My problem is I have a public namespace, whose mail is on a different filesystem than user mails. Some users are allowed to expunge on this shared mailbox, but lazy_expunge is stopping that from working since the mail has to cross a filesystem boundary to make it into the lazy_expunge namespace (location is under the user's home directory).

As a workaround can I run a daily cron job to remove messages with the \Deleted flag on them? If so how do I find them?

thanks -frank