You have to remember that if both of you are hitting down the line, you are both giving up positioning on the other side of the court. If you can hit a short angled backhand topspin or slice to his forehand, now you can camp out over in your backhand corner opening up more room to hit a forehand. He may then be pulled so far off the court, he can only get the ball down the line to your forehand. If he does go back cross court to your backhand, then you could try a backhand down the line to his backhand and he should be on the dead run trying to hit a passing shot.
Another tip: watch Rafa play Fed.