Prevent cupping and splitting of wet PT deck boards?
Ideally a person would hold off using freshly treated lumber and let it dry out in a controlled stable environment. At this point, after installation, I think I would try to keep it out of direct sunlight. If at all possible, put up some sort of a sunscreen to prevent the rapid drying of the surface. You might even go so far as to lay down a lightweight, fast drying carpeting while the wood dries out.

If it's drying out that quickly, I see no reason why you wouldn't go ahead and apply a good quality penetrating sealer. The wood will continue to dry out from below and the edges over time, but at a slower, less damaging rate.