When you configure their sessions select “Specify workstation ID” then enter the device their device description in the field below. If they need to configure a second configuration if you want them to be able to open a second session and so on.
Sound like a make work project to me though…
You need to read and understand Using Telnet exit point programs. Review the topics around that one and look into the Device initialization exit program and the Examples sub-topics.
Make SURE that you understand. These and related exit points can open your system entirely if coding errors are made in the wrong places.