There are probably a few different ways to cobble this together, but hanging from the
cyc pipe sounds like the easiest way to go. I'm hoping its at least corrugated cardboard and assuming its JUST card board with no framing behind it.
You could take 1/16" aircraft cable and do a vertical running stitch through the cardboard itself and run it up to the pipe. That takes care of holding it upright, now comes the issue of unsupported cardboard wanting to curl and wiggle and generally being awful for building scenery.
Gaff tape the bottom to the
bottom pipe of the
cyc. That'll provide rigidity to the bottom. For the top i'd
laminate some strips of 1/8"
luan to the shape of the buildings with contact adhesive to add some support and keep it from curling/warping over time. Make sure to offset all the seams from the cardboard seams. It still has the potential to sort of sag, but the
luan might help...
This isn't ideal at all but you gotta work with what you have, and it'll save your multi-thousand dollar
drop from damage