I mentioned before that supernatural forces were not required, and it seems to me I should emphasize this - it is possible that the player could precommit themself to only taking Box B (perhaps even without checking the contents), and have sufficient willpower to actually do so when tested. If such a person were examined by the Predictor, the Predictor would be obliged to leave the million in Box B in order to win.
It is not implausible that such a person could exist, and it is not implausible that a Predictor might be skilled enough to identify such a person beforehand.
On further thought, a clarification:
It is not implausible that such a person could exist, and it is not implausible that a Predictor might be skilled enough to identify such a person beforehand.