Conditional include based on virtual host ?

Hello, I have developed a large web application the contents of which (language and data) depends on the URL the site is accessed from, e.g. en.site.com would display the "english" site, and "fr.site.com" would display the french site, and so on. The whole thing is "parameterized" through a set of global variables (or defines) that reside in a file called settings.php. The question is: how can I include the "right" settings.php file, depending on the virtual host used to access the site? This is an Apache server on Linux, and I thought setting the "include_path" for every virtual host in the <vhosts> section of httpd.conf would maybe do the trick ? Thanks !