Check out the host-node map stuff. This lets you point an arbitrary host to an arbitrary subsite.
Then check out acs-subsite. This has a default master template and also calls the site master. For a simple customization such as you're discussing setting the header/footer info in the subsite default.tcl template adn passing them as properties to the site master would work. Of course the site master would then create header/footer info unless it already existed.
