samba - Mar 2006 - User authentication without password verification

I have several Windows users who want to access my Samba server and can't
synchronize the passwords with a LDAP server.
Is it possible to define a list of usernames which are authorized to access
Samba without checking their password and map all these users to one UNIX user.

I could archieve this by enabling guest access but then I have no control of who
will access my server.

Is it possible? How?
Any idea?

I am using Samba 3.0.10-1.4E.6 running on Redhat Linux ES 4 EMT64.

Thank you.

C?dric