[Dovecot] Mixing LDAP and static

I want to read quota size from LDAP, but I have a static value for home. How can I mix these?

Right now, I have this LDAP configuration:

user_attrs = uid=home=/var/mail/vhosts/%d/%n,gosaMailQuota=quota_rule=*:bytes=%$M

which works fine, but looks up the uid attribute needlessly, and is not scalable: I have to pick a different, always-existing LDAP attribute for each static extra field that I want to set.

Is there some LDAP configuration syntax like the SQL "SELECT '/var/...' AS home" ?

Thanks, Anders.