@LL1 and @oscarsantis - I just got my remote netsend working with ngrok - it wasn't too hard to set up in the end! As an example of what you get when you run
./ngrok tcp 4000is
Forwarding tcp://2.tcp.ngrok.io:15524 -> localhost:4000- this gives you the clue to what you then need to setup on your 'netsend' on your remote pd patch (with you local simply setup with 'netreceive 4000' ). So then on your remote, the message box coming in to 'netsend' wants to read 'connect 2.tcp.ngrok.io 15524' (ip and port number respectively).
I tested this with one laptop connected to my wifi, and with another connected to a mobile phone running a 4G hotspot. The next test it too see if it works with someone in Japan! Hope this helps