Per IRC discussion, i was refereed to:
Actions"add an action in your build step (thinking about what it means when there is already one, same build step twice, and how to handle that), then check for an action of that type in the post-build step"
"in perform(…) of the build step: build.addAction(new MyAction()) ; then in perform(…) of the publisher: build.getAction(MyAction.class)"
Requires more investigation and an attempt to get working, will update if i run into issues. Thanks Daniel :)