Hostage on oil rig platform

I am on the oil rig, helicopter platform. I have one hostage that follows me wherever I go. There is one other hostage that remains kneeling on the platform. How do I get the one who keeps following me to remain on the platform while I go set the satchel charges to blow up the missile launchers?

Are you to the Middle from the the Helicopter platform gone?
anywhere there should one Area Trigger be.