I basically made my own L-square out of a manila folder. I used a manila folder because it's thick enough to be sturdy and used multiple times, but thin enough to lay flat with the cover I'm scanning. It seems to work for the most part. It definitely keeps the scan away from the edge so you don't lose any part of the image, and it makes it easier to keep it straight. It can still be a challenge because sometimes stuff likes to move as you close the cover.