Following the advice in the link in @Thomas' answer, this is how I dealt with this;
In my dynamic virtual host directive in httpd.conf, I added this php prepend;
Then in the root of my uat directory, I saved a little file that is prepended to all requests met by the dynamic virtual host entry (not all hosts on this server are dynamic, and I don't want to mess with the other ones). In it, I put this;
$path = explode("/",str_replace($_SERVER['DOCUMENT_ROOT'],"",$_SERVER['SCRIPT_FILENAME']));
$_SERVER['DOCUMENT_ROOT'] .= "/" . $path . "/" . $path;
This works for me because my VirtualDocumentRoot is two levels beneath my httpd document root. If yours is any deeper, you will need to adjust the indices of the $path array.
Hope this helps others with the same issue...