Seems pretty simple to me. Put one of those info banners at the top of everyone's Facebook feed (like they did to say "I voted" during the election) that gives

Seems pretty simple to me. Put one of those info banners at the top of everyone's Facebook feed (like they did to say "I voted" during the election) that gives you the option of either opting-in to ads (and ads to friends) or paying a fee to use Facebook.