Craig,
It's possible to do this using the CSS selector syntax in an event-based rule. Set the event type to "element exists", and then use a selector like this:
div.hiddendiv[style*='display:block']
What this example does is looks for a div with a class of 'hiddendiv', and makes sure that the style includes "display:block". You may have to tweak this approach depending on how your site developers are hiding/showing the elements, but something similar to this should accomplish what you need.
Hope this helps!
Best,
Shawn