Authenticate Postfix through Dovecot with slightly different LDAP settings

Hi,

I'm setting up a server with Dovecot (2.2.2) and Postfix (3.1.0). Dovecot authenticates against LDAP and Postfix uses Dovecots SASL. That already works fine. But I would like to have slightly different LDAP settings for Dovecot and Postfix. Current setup:

passdb { driver = ldap args = /etc/dovecot/dovecot-ldap.conf.ext } userdb { driver = ldap args = /etc/dovecot/dovecot-ldap.conf.ext }

Excerpt from dovecot-ldap.conf.ext:

user_filter = (&
(objectClass=gosaMailAccount)
(allowedServices=*I*)
(uid=%u)
)

I wanted to have sparate LDAP filters (allowedServices=*I* for Dovecot and allowedServices=*S* for Postfix), to be able to disable SMTP and IMAP independently. Does anybody know a way to separate those settings?

Thanks in advance, Jakob