I tried that approach but it is problematic - it is very hard to get the application into the proper state that shows the object (maybe impossible without a complex multiuser run). When I drop a Generic Object Action into the script it requires that I pick the object on the application screen. I can't do that - I know the Xpath selector for the object, but it is not currently in the DOM. The step will not let me specify JavaScript or XPath until I pick the object... but I cannot pick it because it is not there.
I am having some conceptual trouble with this - the target object is selected by the JavaScript, but it seems the step itself is associated to some specific DOM object even if the JavaScript is modified (and returns some different object). Is it not possible to break that association and associate the step with a different object (as defined by the JavaScript, not by picking it on the screen)? In this case, the object does not (at script writing time) exist in the DOM. But I know where it will be at run time. Is it possible to script such a case?