Mercury Pantheon vhosts

We have a mercury server setup on VPS.net that is using multi-site to run multiple sites using the same Pressflow install. We recently ran into a problem with implementing our non-www to www canonical domain redirects. In the past we were able to uncomment the section of the .htaccess file included by Drupal to do these redirects because we were not using multi-site. Now that we are using multi-site we have tried to implement the redirects using apache vhosts but the redirect never seems to happen and it appears to be some kind of interference from Varnish that is keeping it from working.

I'm attempting to use a Mercury stack as a server for 2-3 sites. I have separate codebases under /var/www (some pressflow, some drupal). I have vhosts setup with the NameVirtualHost myip:8080 in default and the appropriate vhost files in sites-available with a successful a2ensite. I get a "Forbidden 403" unless I manually insert :8080 in the URL. I suspect Varnish but is there a simple setup guide for vhosts with Mercury that I haven't found with search engines? Is Varnish compatible with name based virtual hosts? Thanks.