I havent mounted my card yet, but I had to use a clamp for my gt 710. Sometimes you can take off mounting hardware and build a platform on the mobo and then actually place the pot against gpu, so it pushes a little and try and reinforce behind gpu, not great for mobo slot though. it's worked for me before. Maybe zip ties to tighten a bit.
Did you try the g92 mounting holes, gotta look at my card when get home, havent taken out of box yet.