Well the jedi masters do talk about how he was never the strongest in the force, but was always a natural leader because of how easily he forms force bonds (which of course lead to his downfall at M-V).
People seem to forget how several characters throughout the whole game (atleast as a lightsider) talk about how the exile can become whole again and the wound in the force he carries with him can be healed as he heals others.
Of course Kreia doesn't like that idea very much...
Now as for weither or not he's using the force directly at the start of the game, he is, but the force is very weak in him because of the wound. Imagine the Exile on one side of a great divide (like the grand canyon), and the force is on the other side. He can still hear it, but it's (to barrow from the game) like an echo at the edge of his hearing. He might be using his force bond with Kreia as a crutch at this point, but I don't think that lasts for too long.
IMO (mostly because I think the Jedi Councel consists of fools and morons) as the lightside exile progresses through the story and starts calling upon the force again, he reconnects with and heals himself so then the divide between him and the force lessons.
The Darkside exile feeds off of those he vangishes, and progresses down the same path as Darth Nihilus.