Hmm.. So you want to have the first click from any window that's just been opened to do something different than anything else?

You could modify (in javascript) all links on the page to add a parameter that sends that info over to the server side.

Normally, the server will not know or care which window is requesting what. That way, people can - for instance - copy the url from one window to the next without surprises. If you want to break that, you'd better have a good reason for doing so.