Seems like a wrapping jig is also a spine finder. Was trying to fix some threads and my darned blank kept rolling on me. Took a bit for me to realize it kept rolling to the same spot. Tried a support at each end of several more blanks, and they sure seem to orient to the 'spine'. A few did it all by themselves,,, no hands required. Then others I just pressed the center with a smooth plastic burnishing tool and they rolled to the spine.
Easier than 'dancing' with the rod and trying to mark the spine, or building another gizmo to find the spine. I have bearings on my supports, but would think any supports should work that are nonabrasive

It's not rolling to the spine, it's rolling to the low position of the blank's natural curve.

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For the couple that rolled on their own, perhaps. But when pressed in the middle 1 Amtack, 3 PabBays, 1 Daiwa, and 1 Lamiglas all happened to roll to the same line I drew on the blanks using the tip to foot method?

If you're pressuring it, then you're probably okay.

One note - the natural curve of the blank usually is along the stiffest and straightest axis. Many of us build around that rather than the spine.

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There is another reason for mounting the guides on the stiffest axis that I think that many do not consider and that is sensitivity. Sensitivity goes up with stiffness therefore mounting the guides on the stiffest axis will result in the maximum sensitivity.