Attaching an image to a moving Green Screen

The solution is layers and tracking. You will have to track the left side of the paper and the right side, then attach each side to a copy of the video. I would suggest corner pin tracking in Mocha. If the paper curves when it is torn, which is likely, you'll probably also need to add some distortion effects and maybe even a shadow or two to sell the effect. I probably would not use a green sheet of paper unless the shot was very long because roto on just the fingers wouldn't take very long and a sheet of paper with some a good cross hatch on it, maybe lines about 1 inch apart, would give you more information to use to bend your video to match the bends in the paper. A green sheet of paper, even with some tracking marks on it will only save you the roto time and the shot will look more fake than if you have a grid to work with.

I'd probably use this technique on both the left and right side of the paper: