Aw dang. Noted. If the natural/added light were constant across the images I'd say copy the changes directly from one to another and use curves to match the brightness. But that's not the case. Hm.
I am unsure if evern ScriptingListener will help you, but here's a startingpoint:
http://www.earthboundlight.com/phototip ... tener.html
It's hell to use and I hate every second of using it, but if you do it methodically you might get some results.
Basically: Do something, read through the logs, copy relevant snippets to another document, delete logs, then repeat.
I am by no means any good at using ScriptingListener though, so I won't really be of any help. I don't know how to get ScriptingListener to get multiple instances from an action index or anything like that:/
Add the snippets to a .jsx-file, then run that file and try it out. Probably won't work on the first try though. Sorry that I cannot be of any further help:/