Don't let him get into a groove:
1) Don't hit the same spin twice in a row. Mix in low-bouncing slices (hard for a tall player to work with consistently) and sharp-angle topspins and go for an 80% flat shot DTL when the court is open.
2) Move him to all four corners of the court, up and back as well as side to side.
Attack him by:
3) Dropshotting and lobbing.
4) Chipping the return and following it in to the net.