It's popular to pose gotcha scenarios like this, but it's beside the point IMO. There are all sorts of things I'd be willing to do for the sake of my own self-interest that I'd freely admit are wrong in the Kantian* sense of the word. Would I waterboard a suspected terrorist to save my son's life? Sure, but with the expectation of being punished if I were caught. I would never support enshrining the practice as law.
Quote: Muller said Wednesday that he'd have no qualms about seeing waterboarding used if it would protect his young daughters.
* "Act only according to that maxim whereby you can at the same time will that it should become a universal law."