I added vanilla to a porter by taking the beans, dipping in Starsan, slitting lengthwise and then dicing with a sanitized knife and cutting board. I added to secondary and racked the beer on top. I let it sit for about 5 days, at 5 days it was incredibly vanilla-ey. It has greatly mellowed as it aged though.
Primary: Apfelwein, Raspberry Lambic, Experimental Wheat cider, IPA
Keg 1: Hefe
Keg 2: Irish Stout
Keg 3: Peach Kolsch
Keg 4: Empty
Bottled: Bourbon Vanilla Porter, Chocolate Stout