Just brewed up a porter and going to be transfering into secondary tonight, I also want to put vanilla beans into the secondary. The question I have is how to make sure that the beans are sanitized correctly.
I make a Bourbon Vanilla Imperial porter recipe that's pretty popular. When the primary fermentation is done, I split 2 vanilla beans lengthwise and scrape put all the "gunk" inside. I chop the pods themselves into 2-3 in. long pieces then add the "gunk" and pods to a secondary fermenter and rack the beer onto it. Start tasting it after about 5 days. When it reaches a bit more than the level of vanilaa you want, rack it off the vanilla and package. You want to atart with a bit more vanilla flavor than you think you want bcause it starts to fade fairly quickly. Between the alcohol and low pH of the beer, you'll be fine with no further sanitation of the beans. I've doen it dozens of times and never had a problem.
Boiling them in enough water to cover them for a few minutes should do the trick, however the results may not be as you intended.
I would suggest making a strong vanilla "tea". Chop up all of your vanilla beans, and boil in about 1 gal of water until it tastes like you want. Strain out the beans and drop this into your secondary once it has cooled sufficiently. If you just add them directly, the flavor of the vanilla bean may not be extracted properly. Also, carbohydrates -> CO2 + Ethyl Alcohol is not yeast's only metabolic pathway. Your yeast may consume other compounds in the vanilla bean, which may produce by products (flavors) that you do not expect.
If that sounds too involved, or you don't want to add that much water to you beer, you can remove the beans after an hour and boil the solution down further, or you can use vanilla extract.