Terry was pretty close in describing how I turned the piece from my last post. The sphere was roughed between centers and I then used cup chucks on each end to fine tune it. The nose of this live center cap was flattened and used to apply pressure from the tailstock to the cup center used to drive the piece from the headstock.
The cup center for the headstock is some scrap that was screwed to a faceplate.
There is a slight cup in the center, the size isn't really important, as long as the sphere makes contact around the rim before it bottoms out in the cup.
The cup was then moved off center by simply unscrewing all of the screws but one and then rotating the faceplate before driving them back in but in different positions. This effectively moves the sphere off center so the V groove can be turned.
Lastly a jam chuck was turned so the piece could be hollowed through the opening created by the groove. The fit has to be pretty good, like the cup center above the contact has to be around the outside before the piece bottoms out in the center. Green wood was used because it's a little more flexible.
Below is a quick video I took showing the cup center on the faceplate in the off center position. It's a very simple solution that I picked up from Christian Burchard. The flat on the face of the live center cap was just wide enough to apply the pressure needed to drive the sphere.
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