Ken, thanks but the issue is that if the plugin does not have a action assigned to that feature then that wont work.
In this case the photo plugin does not have a "view full size" action assigned to the role permissions so trying to capture that event would mean a mod to the photo plugin. And even adding a listener.
The only other way i can even think of is (stab in the dark) possibly with some specialized js and css it could be trapped but it would take someone alot better at js and css than me. Then that code could be added to the oxwall header or footer field, and the css to the custom css field without modding the plugin, but as i said this is a stab in the dark.