Can Windows Authentication logins be disabled on SQL Server 2008 (or R2)? So we can do Windows Login or Mixed Mode, but can we configure SQL Server to only use internal logins and to block all Windows Logins?

Is the only solution to add all potential Windows logins and set them to restricted privileges as a preventative (or reactive) procedure?
As far as I'm aware it is not possible to disable Windows authentication on SQL Server 2008 + R2:

http://msdn.microsoft.com/en-us/library/ms144284%28v=sql.105%29.aspx

The only Windows accounts that will have access are those that are explicitly added as logins (or are members of a group which has a login).