Option 1. Bring them closer to the net. I don't see many moonballers that play the net. You may have to try a few risky drop shots to do this or some wicked forehand slice. Once they come in make sure you are atleast halfway between the service line and baseline so you have the option of an overhead or a swinging volley.
Option 2. Pound the living crap out of the ball. They will eventually hit one short and you should take the ball off the court with a short quick angled shot.
Donnay Pro One 97 w/ Solinco Tour Bite @52lbs.
Donnay X-Blue 99 w/ Solinco Tour Bite @53lbs.