The hottest summer activity among wealthy Meadow Lane residents seems to be sneaking peeks at Calvin Klein’s nearly finished Southampton mansion while the designer races to complete the project by Labor Day. “He’s spending 10 hours a day installing personally designed furniture into his glass house, which has ocean and bay views,” a spy said. Despite “No Trespassing” signs, “Even billionaire neighbors keep biking up the driveway to peek.” A spy added yesterday, “There were 27 cars and trucks on the site with workers. Calvin kept emerging from a black Porsche to crack the whip. People are praying he’ll finish so he’ll have a Labor Day party.” (Klein’s 2004 housewarming for a previous crib remains one of the area’s legendary affairs.) Klein took a Sunday break at Larry Gagosian’s Amagansett home for a VIP screening of Wong Kar-wai’s martial arts movie “The Grandmaster” with guests Renée Zellweger, Terry Semel and Georgina Chapman. Ingrid Sischy was heard saying the arty kung fu film was “a knockout — literally.”