RPF PREMIUM MEMBER
There are two easy ways to do it without vacuforming. Cut out the pieces out of thin styrene and use your fingers and fingernails to round out or 'bubble' each piece. Basically rounding it out with the pressure of your fingers. It's what I did on mine.
Or you can cut slices in the middle of the pieces so they split apart with the curvature of the sphere. But you will need to fill them in afterwards.
The SPLIT method was how I did it in the Article...all those years ago. Probably before some of you were born. hahah