[Dovecot] Overlapping userdb/passdbs

[James Devine]

I have an ldap server for which each entry includes the email address and
the username portion of the email address for authentication.
 Authentication works by username if the username is unique among all the
entries.  I need to now add some users which must authenticate even if the
username is not unique.  I figured one way to do this would be to add a
second user/pass db which puts further restrictions on the ldap query to
make it unique for those users.  This doesn't seem to work however as if
the user is found in the first ldap query but the password does not match
it does not try the second.  I would use the password as part of the query
but this setup requires me to allow the client to hash the password.  Is
there a way to do this?  Or maybe I am approaching the problem wrong.