Abuse his backhand. If he's a 2-hander he almost definitely hits a flat shot and will not be able to create enough topspin to hit acute short angles. He will be forced to hit to the long part of the court - ie. a standard cross-court angle.
Even if he's a 1-hander, he'll struggle to get enough topspin to get angles on his backhand, unless he's an extreme-grip 1-hander, and those are very rare. And if he is, slice his backhand.
in fact, slicing in general (to either his bh or fh) will make it difficult for him to angle you off the court as much, because he has to hit even more topspin to counter your low slice if he wants to get the same angle. If he hits a lot of spin in general he probably has an extreme grip(s), so slice is doubly good as low balls will be awkward. Unless he's Nadal.
In summary: abuse his backhand, slice low to his backhand, slice low to his forehand, and keep hitting to the middle if all else fails.