It was only a matter of time. Only a few days have passed since TMO reported on Apple removing iTunes music sharing support for computers outside your local network and someone has already found a workaround.
A tutorial at lostboi.com offers instructions on how you can resume outside sharing using either the open source utility mDNSResponder or Rendezvous Beacon, which is shareware. The concept is rather straightforward and uses a common networking technique, not an iTunes hack, to fool it into believing the stream is originating from inside the local network.