Do you have a garage? A board propped up against the wall on an angle can help you with volleys. Ceilings high enough? Shadow swing a serve or perfect your toss.
Get a soft kids ball, practice catching ball on the racquet then hit back to wife, ball can't hit the ground. Lots of things you can do, especially cardio and hand/eye coordination wise.
Footwork...get some cones, you'll find lots of footwork drills without hitting a ball.
Few years ago we got a ping pong table, forced me to keep myself low, also a great cardio workout.
I feel your pain, but doing absolutely nothing is far worse than doing something for that muscle memory.