You want to connect to other machines within their LAN for development and to diagnose software integration issues. The customer allows you to connect to multiple devices within their network, but they don't want to install Dull on every machine. You have one machine that you can install Dull onto.
Use the Operator duct type, to create a network gateway capability. The Operator-Server is configured on the one machine on the remote side. The Operator-Client is used on one or more Tunnel configurations on your support side. Each tunnel has a different configuration of the Operator-Client, each one points to a specific host and port. This can be combined with other ducts to provide auditing and logging