It’s on the list for The Civil Nodes.
But Pay Items, is that not available in Camber?
Else, it is a bit tricky but it works, you can send a command like this:
Actually you make two Command Line calls. The first one is to select an object by Handle, so you can replace the hardcoded handle in that Code Block with a parameter, to be more flexible. The second line adds XData to an object. The “L” is to select the last object, which you have selected in the previous command by Handle. The empty line closes the XDATA command.
You can’t replace “L” with the Lisp call, the XDATA command itself is Lisp and you will receive an error.
In the drawing, this is the result:
As said, it works… (But I would not rely on that too much 
)