If your ClickGUI is modular it will make this much more simple.
Assuming each category is rendered independently you could start at mouseDragClick() since this is where the dragging begins. You have to save the start position and use trigonometry to determine at what angle it should rotate. You also will want to cap the angle so it doesn't keep rotating as it gets dragged. There's plenty of tutorials online about basic trigonometry and glTransform and glTranslate which is all you need.
You could use the same logic for animating other things like easings to smoothen the rotationAngle.