My method is automated, Even the people who connect to these remote devices in many cases dont know anything about linux, or security. So with a bit or code i wrote, When you SSH to the SG-1000 it automatically redirects you into telnet to the proper device, no need to issue any telnet commands, etc. You SSH, and its as if you have gone directly to the telnet device in question.
The SG-1000 would also take the place of the firewalling of the crappy DSL Modems, as they could be put in transparent mode, and the pfsense then utilized for a much better firewalling solution and access control.
It would be a simultaneous upgrade to the firewall, and the telnet device at the same time, as well as facilitating better security for any other devices connected in that location.
My code supports tunneling each user account to a different telnet device, not just 1 telnet device. So its flexible in its usage, and works on bigger models as well, such as SG-2220, and 2440.