[Dovecot] Virtual users vacation notices and forwards

I'm in the process of moving from UW-IMAP to dovecot. I'm exploring the idea of using virtual users with dovecot and storing all user information in LDAP. While bouncing this idea off of a coworker, he asked me how we could handle vacation notices and forwards. Currently, we're using a procmail recipe to generate the vacation notice, and the sendmail .forward file for forwards (although most of our forwarding takes place elsewhere so the .forward file is rarely used). These are, of course, dependant on the user having an account on the mail server. How are those of you using virtual users supporting this functionality?

Thanks!