[Dovecot] user name before and after authentication

Hi,

I am new to dovecot and spend the last few hours trying to configure it to my liking.

I am using version 1.0.2

I have a setup where I only have "virtual" mailboxes in various domain ( mydomain.com, mydomain.biz,...). I setup Exim to deliver the email into <some path>/domains/<domainname>/<user>

Now I am trying to get dovecot to access those mailboxes

I setup LDAP bind authentication against an AD server. it works fine... but

I have a problem getting the correct path to the mailboxes.

The user logs in as user@domain.ext

	The mailbox path being at  <some path>/domains/%n/%u 

The LDAP module gets the DN for my user and verify that it can binds, and in 
    the process changes the "user" to  
	cn=<real name>,cn=Users,dc=domain,dc=ext 

	There goes my path

To make matter worse, the uid and gid are the same for all users and are 
fixed (exim user and group). Hence cannot be retrieved from AD

I tried to use userdb static, but I can't seem to be able to reset "user" to its pre-authentication value

userdb prefetch/ldap  but I can't set the uid/gid

So here are my request for help...

Is there a way to set home dir/ mail dir before authentication?
Is there a way to reference the pre-auth user name?
Is there a way to create arbitrary variables and used them?
Is there a way to fix the uid/gid to use to access the mailboxes?

Any one of these could probably solve my problem.

Any suggestion is most welcome.

François