Hi, sorry for the late reply.
To directly answer your question, as I have mentioned before you would need to create an interactor with FixationDataBehavior, but it is not enough to just create it. You would also need to push it through creating snapshots on every query from the Engine. So basically to achieve just that you would need to write your own implementation of EyeXHost. Otherwise, snapshots are committed without your notice.
But if I understood your goal correctly, I would say that achieve what you want will be a bit hard with Fixations stream, because of the “shaky” nature of the gaze you will never be accurate enough. What you can do, is identify, say, with FixationsDataStream where user looking at this moment of time, show your screenshot on the newly created form, for all areas user can interact with create an interactor, most probably gaze-aware interactor, and when it is time to get back to the original screen just select the element user has gazed on before.