[Dovecot] Using account alias as login

Hello, I use dovecot with a LDAP backend for user account and aliases. The aliases are objects of the class couriermailalias. Some users would like to use the alias address as POP/IMAP login instead of the 'true' account. Is this possible?. I am using dovecot version 1.0,10, from ubuntu hardy packages.

Thanks for any answer, Javier