South Korean pop sensation Psy and Diana Ross have signed on to perform for U.S. leader President Barack Obama and his wife Michelle at this year's Christmas in Washington concert. Psy, who performed for Thailand's King Bhumibol Adulyadej on Wednesday (28Nov12), will close the 9 December (12) gala with a performance of his Gangnam Style hit for the Obamas at the 31st festive show. Demi Lovato and American Idol winner Scotty MCCreery are also set to appear at Christmas In Washington.