How about keeping it simple.

Level 20 Corrupted Authority. Familiar
Your mastery of the flows of corruptive influences in sorcery is to the point where you always have a Summoned Demon at your side that does not count in your follower limit. It functions and levels like a normal Summoned Demon but without any timer associated with it. If it dies, a new one is immediately summoned in a ball of Orange magic (the summon animation) and immediately follows you. It will ALWAYS follow you and you cannot put it on scouting or remove it until you remove the perk. Once the perk is removed, it disappears.