BRITNEY SPEARS served up a birthday treat for husband Kevin Federline in Las Vegas, Nevada on Thursday (23MAR06) - a Cher impersonator. The couple have been living it up in Sin City this week for Federline's 28th birthday and Britney decided it would be fun to make her man think she had booked pop superstar Cher to perform for him. Celebrating after hours at hip venue Tao, Britney, wearing a white fedora and a sexy black lace print shirt and jeans, arranged a surprise. A pal stepped up to the club's microphone, wished Federline a happy birthday and introduced 'Cher.' A stunned Federline chuckled as a larger-than-life female impersonator stepped out on stage and sang along to Cher's IF I COULD TURN BACK TIME. A little person, dressed as a mini-Sonny Bono then joined the act to sing I GOT YOU BABE as the crowd roared with laughter. A fellow reveller says, "It was a special birthday indeed. Everyone found Britney's surprise really hilarious. Kevin and Britney and their friends were in fits. "Kevin finished the night off by dancing to his wife's I'M A SLAVE 4 U and then hitting the DJ booth to play songs from his new album."