This is probably as difficult as it sounds, but some duct tape may work to support the edge of the hole temporarily. You would need to pull the plant out a bit, dry the surfaces, set the tape and then put the plant back in.

If you had a 3D printer, you could probably make a temporary ring for the hole as well.

If you don't like the idea of random 3D printed things or even duct tape, try to wrap the top of the cup in a layer or two of thin fabric from a tee shirt.

The goal is to make the hole a bit smaller or the cup a hair bigger. Wedge something in between the pot and the lid, is what I am saying. (Hell, you could even rig a few nails to act as a wedge.)

If you have a 3D printer, it would literally take me 5 mins to design some kind of split-ring thingy in CAD to support that plant.

(I did DIY hydro grows for a while, so I sympathize with the issues you are encountering.)

Edit: Yeah, it took me about 5 mins. However, the design is untested and will likely need some sanding and trimming to fit custom hydro rigs: https://www.printables.com/model/866113-net-pot-support