Maybe I am wrong on this, but I think the q3dirtrav was not fixed by IW in CoD4. So it's basically possible to download any file from the main folder of the server and from the fs_game folder as well, including gscs. Also, at least in CoD2 you can, as a client, simply hex-edit your multiplayer .exe and change the part with '_svr_' to for example '_sxr_' and the client downloads that .iwd automatically.