If you have a drawing of the windows in the right size with the details of the panes (I mean the little squares that would be the glass panes) you could see if a laser cutter could cut them into the thinnest plywood you can find and then lay them in behind the metal frame. Then use either clear plastic sheeting (or translucent depending on the look you prefer) and glue it behind the plywood to simulate glass. I did something similar for the Mantua Soleil Royal and it turned out well.
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