[Samba] Link AD to pre-existing UNIX accounts

[CG]

I'm trying to use winbindd to enumerate and link AD users to their pre-
existing UNIX accounts. Right now, winbindd creates new "users" for UNIX based 
on windows username and groups.

What I can't figure out is how to explicitly map the AD users to their pre-
existing UNIX accounts. I'd like the users to be able to access their UNIX 
accounts with their UNIX authentication information /and/ their AD 
authentication information. I had hung my hat on the "username map" smb.conf 
directive, but I find now that it doesn't apply to winbindd.

Has anyone worked out a strategy for this scenario?