I have that HF unit, and don't have any trouble keeping the lens cover up. I just push a bit harder when I open it, and there is sort of a click, allowing it to open a bit further and to stay open. I just looked at mine, and there is a small molded bar that causes that first stop, and when I push harder that goes under the plastic stop from above. If you have that bar, and it's too high to go under, then try sanding it down a bit so it can.
Also, I had difficulty gripping the short tab at the front of the cover to open it, so I just put a piece of clear tape on it, going from the back, making a "U", and then fastened to the front of the existing tab. It's longer than needed, so it leaves about 1/2" above the tab. Strong enough and easy to grip.
Maybe yours is different, but this works great for me.
