gistfile1.txt

// Redirect to force indexing with custom domain sitemap
$subject = $_SERVER['HTTP_HOST'];
$pattern = '/gotpantheon.com/sitemap.xml$/';
preg_match($pattern, $subject, $matches);
$counted = count($matches);
if ($counted > 0 ) {
    header('HTTP/1.0 301 Moved Permanently');
    header('Location: http://yoursite.com/sitemap.xml'. $_SERVER['REQUEST_URI']);
    exit();
}