LOS ANGELES — Simon Fuller, the entertainment magnate behind "American Idol" and its charity event airing Wednesday, is trumpeting a starry lineup that includes Elton John, Alicia Keys and Carrie Underwood. But he played it coy when asked about the "Idol Gives Back" role of two other prominent people. Bill and Melinda Gates, supporters of the fundraiser since it launched in 2007, "have done something very special, quite incredible, this year," Fuller said.