I've turned many spheres and have combined two techniques to make them perfect without a jig. But at a club demo, I was challenged to turn a hollow sphere. My response - sure. But, here's the proof.
Using the process, I've described in previous videos, the only difference is to stretch out the center of the sphere while still an octagon. In this case, I hollowed the sphere, then glued it back together again. Similarly, I could create friction slip joint or thread the joint. After gluing or joining the halves back together, continue the process from where it was interrupted.
My hollow cherry sphere is 3" diameter. It weights 75 grams = about 63 grams less than a similar solid cherry sphere. The finish is beeswax and mineral oil.