As part of the launch campaign for NBC’s slick new drama “Las Vegas,” audience members at a series launch event in Hollywood, which included a charity poker game with the show’s cast, were offered the chance to win two walk-on roles in the show. Attendees began arriving at 6 p.m. and had to be present to win. But two hours later, when KIIS-FM radio host Sean Valentine drew names, none of the 15 picked were still there. Finally, cast members Josh Duhamel and Molly Sims ventured into the crowd and crowned two winners on the spot. Mr. Valentine also offered to draw two names from the entries the following day on the radio and give away two more walk-on roles. He then gave away four walk-on roles, an NBC spokesperson said. The screening that followed went much more smoothly for everyone-except “Las Vegas” creator Gary Scott Thompson. The bar was closed during the screening, and Mr. Thompson could not convince the bartender to serve him a drink. We assume this means the bartender did not get a walk-on role.