[squid-users] Workaround with NTLM Website and NAT

My situation is simple:

A web site is using NTLM authentication ans ask the user for credentials
(without squid).
Our squid goes out trhough a NAT connection, then when the user tries
with squid configured, and IIS error shows up in the browser saying:

You are not authorized to view this page

You do not have permission to view this directory or page using the

credentials that you supplied because your Web browser is sending a

WWW-Authenticate header field that the Web server is not configured to

accept.

----------------------------------------------------------------------------

----
 
Please try the following:
 
Contact the Web site administrator if you believe you should be able to view
this directory or page. 
Click the Refresh button to try again with different credentials. 
HTTP Error 401.2 - Unauthorized: Access is denied due to server
configuration.
Internet Information Services (IIS)
According my little research NTLM IIS server is rejecting my GETs with 
"Via" header for security reasons.
Is there some conf option to disable Via header ? Is there another 
workaround to this ?
Guillermo