I wonder if you could have an off-screen, inaccessible element on each screen, e.g., a text box, and give it a unique but meaningful and readily identifiable text value, e.g., '!MyQuestion12'. Potentially your javascript could iterate through the html elements on any given screen looking for your hidden element, e.g., something that begins with '!MyQuestion...'. You could then tag/report that unique text value with the feedback left.
Depending on how closely tied your unique text values were to the actual storyline screen (i.e., would this unique text value accurately point to which screen it was), you would either inherently know which screen the feedback was referring to or you could do a simple search in Storyline to find the value.
Maybe there's something in there to help? I've seen lots of examples of iterating through html elements looking for alt texts etc. Good luck!