Just replace your normal ads banners inside your app with a great looking CPA banner offer, that's it, now all fans will be redirected to your CPA offer...
Go to the next level, by creating a Landing Page that is GEO targeted so for visitors from USA it will show USA offer, for users from UK it will show UK offers and like this for all different countries that your fan page have... and for the third world countries that are no offers at all just make something different, place CPM banners or force them to like another page of yours
Cheers