|Leave your opponent hanging!|
photo from wisepreneur.com
If players have sufficient control to move the ball around on the court, this activity will highlight the advantages to be gained by forcing your opponent out of their comfort zone. Let's say one player hits a nice cross court forehand deep. IF the opponent is able to abide by the rules and stay within court boundaries to hit the return shot, chances are good it will be a lousy shot due to the contortion required to hit the shot from a less than optimal position (forced by them having to stay within court boundaries).
Play to a predetermined number of points, or for a set time period. Easily converted to a team activity.