How can I attach an image/clip to a 2D plane (without 2 of its corners)?

Hullo.

I have a simple scene with a moving camera involving a large screen, and I'd like to make it appear as though the screen was playing an image/video of my choice.

However, the shot doesn't include the top two corners of the screen, which makes it harder to pin the perspective properly. Presumably if I knew the dimensions of the original screen (16:9), there would be some way of finding the correct proportions?

Any help is greatly appreciated