Before exiting website, script raises popup to request a Facebook Like (with button)

When a visitor to our website tries to exit from our site (eg navigate to another site, close the tab or browser, etc) we want a script to run to check if they are a current fan (Like) for our Facebook page. If they are not, we want a pop-up to raise requesting that they Like us on Facebook, follow us on Twitter, or join our mailing list. The popup would have a direct "Like" button, "Follow" button or "Join" button. The popup would need to be the type that is not blocked by most browsers, so not a "true" pop-up, something else. Our site is built in Wordpress and PHP. You MUST have done something like this before and please prove this by either showing us an example, or at least describing how you plan to implement this. We need a fast turn-around on it, like a few days.