That is exactly what I want to do. I am setting up a GMV clone and would love the soft top cargo cover capability.
Maybe just cut down some bows? How do you seal it against hard top? Velcro on Hard roof?
The vinyl wraps overtop the C Pillar cross tube, with slots cut for the 3 bolt/bushing assemblies, under the tin roof. There was a rubber seal that went between the C Pillar and the tin roof, so a strip of closed cell foam between the vinyl cover and the tin roof would not be out of the question.
Mine, I would repurpose some HMMWV cargo bed bows or custom bend a piece of 3/4" conduit to cross between the two D Pillar cargo panel brackets, held to the top cargo panel bolts with a P clamp on each side. The issue cargo cover kit only has the hinged bows at the front and rear of the cargo bed, so I don't think it would be necessary to drill holes in the center of each cargo panel for another pair of P clamps to secure a bow in the middle, may or may not hurt, especially in heavy rain or snow climates.
I suppose the rear flap you could sew in some heavy gauge clear marine vinyl for a window like the issue HMMWV cargo covers.