Sadly the few remaining shreds of official technical information aren't documenting the .json formatting, but I'll post them here anyway, as off-topic as they may be. Perhaps you'll see something that my untechnical eyes didn't see.
Also related to the viewer, you may have noticed that 'Share' links have unique variables attached to the normal view page and Photosynth collection ID where, 'i' is the Photosynth projector, 'z' is the zoom level, 'g' is the clump of photos you are navigated to, 'p' is the pan position, and 'm' is whether the viewer is in 2D mode.
I don't know if there's any overlap in variables between the .json file and those used by the viewer, but that's about all I can offer.
Photosynth team, we could use your help here.