I used vanilla to add to my keg of root beer recently, and I've always had good luck with warming the alcohol to near boiling with the beans in it for a faster method- which I would think would pair well with a shorter secondary as well, rather than the month that's being suggested above. Split them down the middle and scrape the sticky interior out into the liquor so it has a chance to dissolve.
Also, I make my own vanilla extract with brandy versus either the flavorless vodka, or the traditional, but too strong, bourbon. True extract takes months to steep and age, but a lot of the top vanilla notes come out within the first days and weeks. You just won't get the depth of flavor and aroma that quickly.
Of course, you could also just make your own extract ahead of time and add it to your beer as liquid flavoring rather than using new beans.
Keep in mind there are also many kinds of vanilla beans. I found Tahitian beans at my LHBS (Brewers Best packaging), which is my preference for their cool floral notes, but Madagascar will be a bit more of a bold flavor, and Mexican beans have a spicier taste.