you can make a mold from the foam but a seat itself is going to be a mess since the stuff will crumble and break over time, even with glass over the top of it. I've made a couple molds for making solid glass seats and they are very comfortable,just make sure to carve out enough extra between your legs and the sides to you aren't locked into place, the problem with the process is you'll make a garbage can pile of detritus compared to carving minicell seats. Wearing a wet-suit and extra sweat pants you can be the male mold for the foam mold in the kayak (garbage bags galore protecting everything) pressing the excess resin too pool between your thighs,,,with med fast epoxy or polyester resin the heat can get a little too exciting.

The other benefit to an 1/8" thick seat was all the room underneath the thigh area for storing easily accesible stuff bungied in.
What I found was the molded seat gave me was good support around the hips and thighs, just from a toxic wasteland standpoint I'll stick with minicell and cover it with fabric.