How can I get Squid's NTLM Authentication mechanism to use Active Directory with multiple domains.

I've gotten squid's ntlm authentication with winbind to authenticate users against a single domain but I can't seem to get authentication against multiple domains working. It seems as if winbind can only join one domain at a time. Using domain trusts I can't list the users in any of the other domains with wbinfo -u. Also it doesn't seem like there is an ldap helper with multiple domain query capability. Is there any way to use squid to query the appropriate ldap or kerberos server based on the domain passed in the ntlm authentication handshake?