Did you try a knife to cut the supports? Or a screwdriver and hammer? The supports would break before the rest of the panel. Unless you hit the panel instead.
I found the same thing. I tried using a razor saw but the gap was too tight even for that. I tried a sharp blade to cut the top of the joining piece but could only cut in a small fraction. In the end, I held the rear of the panel around the knockout piece and gently tapped with a small hammer until it gave up. I think the laser cut should be doubled up in this area, to at least allow a blade in the gap.