qmail-ldap - ldap and local users

Hi all.

I am trying to understand how to solve a problem.
I have qmail-ldap for my domain based on ldap and now i need to use this 
same qmail do receive mail of another domain without ldap (just a few 
users).
The LDAP server is not under my control and therefore i need to use 
local users. However all this new users will have to have their email's 
received in their mailbox "managed" on ldap.
I have searched and made a few tests with virtualdomains, rcpthosts, and 
alias files with no success.
I always get the error that the mailbox does not exist :/
Is there any way to accomplish this scenario?

Best regards

Nuno