No, I'm not sure how you do that. I use Uncle Nick's 2x4 internal beam tooling method.
Seems like I would have to create an external set of forms with allowance for the wood and glass, orient them properly on a strong back.

What you describe was exactly what happened to my deck. However, I know the humidity went from ~40% as I glassed the outside to 100% before I started to glass the inside. When I dried out the inside, as I said before, the curvature was reversed until it straightened out.

My guess is that the wood on the uncoated side picked up moisture, expanded and caused your and my warpage.
Note that I glassed the entire outside surface and it was fine until several days later when huge rains and humidity showed up.

I have glassed or even just coated with epoxy for quite a few years without your symptoms.

Care to tell us what resin you used? I use West.