I did not try the DxDesigner method. However, I was able to use the PADS Part Type Editor to define multiple Gates and associate Pins to those gates. I was then able to create associated nets, add them to a matched length group, then tune them.
It should be noted that I probably didn't set up the Gate | Pin Swap correctly. PADS Layout gave me issues about having no available gates/pins to swap to!
Another point to make, this is in a Netlist flow, so linking the DxDesigner Symbol to the PADS Part Type through the interface is supported unless you're in Integrated Flow.
Here is the result. I selected two of the nets to show how the different segments picked up the tuning:
Now that I better understand how PADS Part Type editor works, I may go back to the DxDesigner method and see if I can't get the setting right to flow directly into the Part Type library during forward annotation ... or convince the company to invest in switching over to the integrated flow!