I've been making some tests, this is actually quite reliable...
The target should be to make this as easy to use as possible, requiring a custom jackd instance is a bit troublesome, but indeed it works.
So coming in v1.4, you can do:
1. on your own pc, run:
jackd -R -P 80 -d net -a 192.168.51.1 --opus -C 2 -P 2 -i 1 -o 1 -l 4 -n mod-slave -s
2. on mod, via ssh, run:
jack_load netmanager -i "-a 192.168.51.1"
systemctl restart mod-ui
The "slave" ports will appear in the web interface, allowing to easily connect things.
If you stop the jackd instance on your system, just restart mod-ui service again.