get into a weaponized car that can enter the avenger
friend gets in passenger seat
hit right on dpad and start at same time to stop from entering avenger
have friend join someone in different targeting mode, accept the first, deny the second.
now when you hit pause and go into the avenger then drive back to your facility your friend will be inside everyone's facility with guns.
he wont show up on the radar in your facility but rather shows up on the radar inside mt chiliad