There is one way to work around this that I can think of. However, it will not make the NPC appear to "beam out" it will simply make it look as though the NPC is no longer where they used to be.
Method: (Which will not work on a transporter platform, by the way.) Have your NPC which you want to "beam out" standing next to a wall of some sort. You can create a trigger that moves the wall so the NPC is on the other side of it. Rock formations do the same job on a planet's surface.
Why would you want to do this?
Because the NPC can say something like, "I'm heading back to the ship." Make the player head to another location/room. "Sir, I found something!" On the way to their new destination, the player will trip the trigger which moves the wall or the rock formation, so that when the player returns to the first room it gives the illusion that the NPC has vanished, when in reality the NPC is just on the other side of the wall hidden from view.
It's a pain, I know, but its the only way I can think of to make people vanish at present. Hope it helps.