Not that I've tried a CP when shooting towards the sun, but a CP is supposed to have greatest effect when shooting 90 degrees from the sun... so I would imagine in this case, a CP would have little to no effect. On the other hand, if nearly all the direct light is blocked, then perhaps all the remaining light in the landscape is scattered from an extreme angle, and a CP would have a large effect.

I think what you need to do is to convince B+H or another quality polarizing filter maker to do two side-by-side test shots during the eclipse, one with a filter, one without, and report on their findings. If it helps, they sell more filters next time. Seems like a wise investment of their time.