I liked the idea of memory debt as I think that consume other people's mind should impact upon yours, but I suppose this could be shown by mental stress
and GM mandate on what memories you can recall.
Maybe we can rule that as a limitation of Mimic Abilities, providing a Rebate of [+1]. The power would work the same, but whenever the Eater used a memory or Power, it would:
A) Invoke Personality Debt.
B) We could rule it like a Hunger Track (call it a Persona Track), and using the stolen abilities causes "Persona" Stress, which makes it more and more easy for the stolen personality to assert itself.
C) We can reskin Demonic Co-Pilot but, instead of a Demon and Demon agenda, it's the personality you just ate trying to turn you against yourself. Instead of taking Mimic Points, you could just determine that "Eaten Persona Co-Pilot" gives you a +1 to its important skills.