Familiars, Animal Companions and Cohorts

Basically I'm trying to figure out how you can make a creature follow your protagonist through "zones" (.are, whatever new areas are referred to in this game). I think I've tried all the different types in EA.IDS, setting them with opcode 72 never let the creature follow my team out of the area. I've seen a few mods, like more styles for mages and a few NPC mods with animal companions that can do this, so I'm pretty sure its possible, I just don't know how.