The con was on for the Nov. 7 world preem of “Gambit” at Leicester Square’s Empire in London.Cameron Diaz, Colin Firth and Alan Rickman retained their clothed modesty along the red carpet, having all stripped for CBS Films’ onscreen heist. Helmer Michael Hoffman tested his own dupe on the crowds, outing Firth as the pic’s voluntary flasher, “Colin is a complete exhibitionist; he’s completely happy to be naked.” A leggy brunette, Firth upstaged Diaz with rumors of the onscreen exposure of his pins. “My legs are there for gratuitous comedy,” he said, modestly closing: “They’ve been shamelessly exploited.” Firth and Diaz went on to divulge further set-based overexposure, this time at the hands, or more accurately, via the rear of Rickman. Their tale told of how an entirely bare Rickman inadvertently flashed London’s office workers on set, baring all in a window-walled office. Fraudsters and guests later hopped over to the Corinthia Hotel for post- dupe drinks.