I've done throwaway ticketing (for last legs) some times, but this is a new variant. Usually it is about not boarding your last leg. In your case it is about leaving from the plane doing your last leg. Is an alternative not boarding the KL flight on the original ticket in Curacao and paying a one-way Curacao-St Maarten instead that is not too expensive and avoiding the security checks/issues others fear here? In a way I assume no one could stop you walking off the plane with your hand luggage, but if indeed then they miss a passenger that has checked-in for the full flight......