You’re very welcome, Dan!
To get there, the suggestion would be, by setting the joint which should trigger it as a relative-path. (Click on the Node and check the Attribute Manager) Which means that the XPresso tag should sit on this Joint.
The PoseMorph could be dragged into a [new] User Data Field, which would then require an additional pulldown menu [User Data as well], which selects the “channel”.
Additionally, a User Data Vector parameter should specify the relative position to the Root Object, which might need to be dragged into another User Data field.
Adjustments for the Falloff itself should be provided in the User Data Field as well. If all of that is faster than to open the Xpresso tag and drag the objects on top of the existing nodes might be worth an exploration.
The XPresso Tag can be saved in the Object Manager> File> Save Tag. While having a proper name, it will be easy to load the tag again.
Much more comfortable would be a Python-script, perhaps you post a request in the CV-Tool-Box.
As a side note, try the “PoseMorph Deformer” (which has a falloff build in and takes the PoseMorph information).
All the best