Require server verification (https:) for all sites in this zone - IE7 Group Policy

I have a Windows server 2003 terminal server running IE7.  I need every user that logs on to the server to have a particular website added to the Trusted Sites Zone in IE and the 'Require server verification (https:) for all sites checkbox must be unticked.  I have found how to add the site to each user using group policy but I can't find a setting for the checkbox.  Does this setting exist?  If not how do I change it for all users?

Thanks