I have a solution for you but how well it works depends on certain factors. I did it for my own use and it is actually quite stable even in windy conditions. The main thing is you need to be able to anchor to the ground so if you can’t drive stakes in, you better find really heavy rocks on site.
I designed the collar myself, 3D printed it in glass beads infused nylon, then fabricated the metal loops that go in the collar. I transfered the level vial from another pole, it’s adjustable with the 3-screw pivot design. The line used is no-stretch dacron so you can get it really tight. Surprisingly, it’s very easy to setup alone and bring the bubble level. I thought it would be harder.
All this is added on a 4-section carbon pole, 1.8m long. The entire kit fits in my 32L day-pack, including the pole, and weights close to nothing.
Video: https://photos.app.goo.gl/9WMSDhDMy3g6gxsf8
(I only used two sections of the pole for the vid)