I'd probably put a damp cloth over top of him for a while longer (in a container). It's not going to get any easier...every time you let it dry out again.
And don't be afraid to spray him with water directly while you work on him....they get rained on in nature, you know.
I don't have long fingernails but I gently use them (after soaking snake) along the edges of the mouth to loosen the old skin. Peel slowly, try
to keep it intact enough so the eye caps come off too, with the upper jaw. You'll have to be persistent.