[Dovecot] LDAP quota groups

Is there any way to have a per-LDAP-group quota? The OpenLDAP folk's suggestions are to hack the source for an overlay (ideal, but it looks somewhat involved) or to do it at the application (Dovecot).

I've added an LDAP userattr 'quotaMegaBytes' which is great for allowing me to override the server's default quota on a per-user basis, but ideally I'd be able to override the quota only for people who are member of a certain LDAP group.

Perhaps I could override it for IMAP sessions with a postlogin script, but I can't see any way to apply it to deliver.

Thanks for any suggestions,

Ian