The moderator should say, “Senator McCain, what is your plan for feeding the hungry children of America?”
McCain should say, “Well, that's an important goal, but I want to talk for awhile about Raila Odinga, who my opponent campaigned with, and all the dead, hungry and displaced children in Kenya as a results of the riots my opponent helped create the perfect storm for....”
Yeah, I thought of the same thing. There is nothing moderator can do to prevent you from saying what you want with your own time.