I use an old screwdriver with the tip sharpened at a slight angle to get full contact in the notch.

Before unscrewing the ball cup, do something to mark one of the notches and mark the nearest spoke. When you re-assemble, make sure these aren't 180 degrees apart due to the double threads. If they are off, reinstall or the wheel MAY need retruing. The bearing surface in the ball cup isn't always exactly concentric with the threads.