After you send the GNUTELLA CONNECT/\n\n string, you could send a ADDGROUP 80SROCK/\n\n immediatly after it. This way, non-enabled servers would dump the ADDGROUP as a fractured packet since is was unexpected and unidentified, but enabled servers would pick up on them. Theoreically, you could add many messages after the initial connect and non-enabled servers would dump them. That way your server could integrate seemlessly into the already existing network and still use the feature with other servers.