If he is actually "aiming", then the only real fix is switching lefty. If he shoots truly instinctively then the mental computer will adjust and compensate. I am right eye dominant and shoot right, but with some of the sunglasses I wear my right eye can't even see the the target. It doesn't affect my shooting at all. I've tested this by shooting with left eye open, right open, or both open. With my style of instinctive shooting, it makes no difference in where I shoot, or how accurate.