I looked all over the internet for corner legs that fit 2020 extrusions. Do you think I could find any? (The answer is "No") Anyway, this is my take on a simple, yet elegant, support system that also raises the machine 120mm.
I also wanted to have the ability to utilize the extrusion all the way around. These legs mount under the frame, so they don't interfere with the sides.
To keep things from sliding all over the place, I smeared some hot-melt glue on the bottoms of the legs and let it cool. That provides a suitable amount of friction to keep the machine on the table.
Attach these to your frame with (2) M3x16 machine screws and hammer nuts. I can't guarantee they will fit all 2020 extrusions, but they should fit the common type (like found on the ADIMLab Gantry).
Be sure to post a make if you decide to use these. I'd love to see it!