I don't have the North book in which I'm pretty sure he made his processing-to-hold-the-sun-in-a-stone-frame suggestion. So I don't know exactly which combination of lintels and uprights he thought might be the rectangular frame. But surely the frame would have had some width, to accommodate lateral movement?

And perhaps the phenomenon intended was not to have any one person hold the sun in the putative frame for a long period, but to allow several or many people processing up the avenue to glimpse the framing over a period of some minutes?

The whole thing needs an experiment, with a few people trying to hold something like a framing for a while by walking slowly up the Avenue, and another group testing the view through Stonehenge from various points along the Avenue.