i was thinkin of the down comforters last night and I think I would clamp it all around the hanging hammock with someone on a diagonal lying in it. using those squeeze wood clamps, adjusting as needed to accommodate all positions and see what I come up with. I was thinking of then marking it and cutting it carefully, taping w/stiky back cloth tape then sowing, no down transfer
allowing a little extra for fasteners/fastening etc
just theory but I will try it one day.
could bypass the tape and just sow then cut of the unneeded side of the seam.
I would just sun/air the quilt instead of washing.
best of luck!