HOLLYWOOD — Dick Van Dyke’s fancy footwork brought the crowd to its feet March 9 at the seventh annual Backstage at the Geffen gala.The 83-year-old thesp received a standing O after singing and dancing to classics such as “Chim Chim Cheree” and “Chitty Chitty Bang Bang” at the fund-raiser, which raised more than $500,000 for Geffen’s Stage for Any Age education and outreach programs. At the Westwood theater, stars of all ages — Brendan Fraser, Dana Delany, Helen Mirren, Carol Burnett, Christine Lahti — shared funny, and often embarrassing, backstage stories. The evening, helmed by Geffen Playhouse producing director Gil Cates, also included a special appearance from a President Obama look-alike who fetched a few screams and a standing ovation before the aud realized it wasn’t the man himself. Mary Steenburgen presented Leslie Moonves with the Distinction in Service kudo and Martin Short intro’d honoree Rita Wilson and spoke of the great high that comes from performing in front of a live audience. “The only difference between you people and pure-grade pharmaceutical morphine is that morphine doesn’t judge,” he said.