Start: Attach the rope handle or EZ-curl bar to the low pulley. Grab that attachment, and sit on your bench with your back to the weight stack. Lift that attachment overhead so your upper arms are perpendicular to the floor, with your biceps facing your arms.
Finish: Lower your forearms behind your head until they're just below parallel to the floor-no farther. Pause then return to the starting position.
Simply do the seated version while perched on the ball rather than on a bench. Just make sure you place the ball close enough to the low cable that you can maintain a near vertical line when you extend your arms, without the ball touching the cable station.