Patience, patience, and more patience
I just force myself to be ultra-patient when playing these types of players. You need to make them work and pay the price for their style of play.
First, tell yourself that every point will be very long so you're mentally ready. Don't give him what he wants, which is easy balls at the baseline--use safe angles. Always realize that the pusher depends on you getting impatient and making the errors. Take that away from him by being more patient then you ever dreamed of. Move the ball around with low risk. Be safe but unpredictable. The opportunity ball will come at some point and you'll have to make a play on it. If you don't, you'll lose the match, which should be the fair outcome, right? If you score on a small majority of your "opportunity balls" you'll likely win the match.