I am not sure I understand the problem... the Twonky server creates localhost URLs in the DIDL and you want to access these resources from another host? How is Cling involved and what do you want it to do?
You can see on startup as INFO log messages which interfaces Cling binds to. There shouldn't be any loopback interface, Cling only binds to regular LAN interfaces by default. So I can't understand how Cling receives a multicast datagram with a 127.0.0.1 callback, unless the Twonky server sends these messages out on a regular LAN interface. This should then be changed in Twonky, obviously. No LAN control point can do anything meaningful with a 127.0.0.1 callback.