So I dumped the beans in the food processor.
I added the beans in place the the margarine the the recipe calls for. This one may have been a bust. The Mac and Cheese ended up runnier than usual, and the beans gave it kind of a grainy texture. I certianly wasn't a fan, and I don't think I convinced Little Miss either. I guess we'll just have to try the half-whole grain and save the bean trick for baked goodies.