Just had a lesson on this. Spent some time on half-volleys from the mid-court -- which is a situation in which a lot of half-volleys have to be hit.
Since I am already inside the court, I should be in my volley grip. When the ball would need to be half-volleyed, the pro had me make only one adjustment. I used my wrist to close the racket face (maintaining my Continental volley grip). Then, with no backswing, I could kind of guide the ball with a follow-through.
I have to say, this really worked nicely. No need to change my grip. No balls that popped way up because of the Continental grip. It was easy to change the wrist a touch. I had excellent directional control.
Now I just have to practice it and own it.
-- Random Error Generator, Version 4.0
-- Master Moonballer