My parents have a hallway in their farmhouse that has a curve to it. The drywallers accomplished this by cutting "V" shaped grooves in the backside of the drywall and suing lots of contruction adhesive instead of screws. I'm not certain that it was the right approach, nor am I certain that this would work for a ceiling. But they haven't had any problems with it. I would take the time to expirement with differnt approaches and see what works best.