Take prisoners. Fatten them up and then send them home.
Show them porn flicks.
North Korea is so tightly run that I don’t think that would work there, instead of injecting a political virus into their society the NK government would merely imprison or kill anyone who came back mentally impure, and they would exam thm upon entry, NK doesn’t play around and allow the seed of anything to start or even arrive, NK is impossibly isolated and controlled.