If the system mechanics are not a problem, then this is really a roleplay question, specifically: "Can that specific player successfully portray two identifiable in-game personas at the same time?"
The majority of burden is on the player rather than the GM. Perhaps it might help to use different accents, or face different directions, like Gollum's mono-dialogues. In a Fate game (Dresden Files), I and another player each had to distinguish between our base PCs vs the co-dominant spirits in their heads. Separate bodies means your player will also have to manage two sets of physical actions, but it's doable.