Since htaccess is not my strong point, i did a php header redirect:
$domain = $_SERVER["SERVER_NAME"];
$requri = $_SERVER['REQUEST_URI'];
if (($domain == "subdomain.domain.com") && $requri == "/" ||
($domain == "www.subdomain.domain.com")) {
header("Status: 301 Moved Permanently");
header("Location: http://domain.com/subdomain");
}
This solution is working like it's supposed to, except from some file submit issues that need some additional tweaks for the subdomains.