Is it possible to use only a part of the canvas of a video file on a 360 photosphere, instead of the whole canvas?

I currently use UMP (Universal Media Player - found in Unity asset store) to output a local or youtube video onto a 360 photosphere, but it's obviously the whole video canvas. Now I have a video file with the canvas split into quadrants, each playing a different video. I'm currently using masks to play 3 of the quadrants on separate surfaces, but I need to use the last quadrant to be used for the 360 photosphere.

I'm not looking for a direct solution per say, but hopefully a direction to start in. I'm thinking a mix of masks and shaders of some kind, but I'm very new to unity.

Any help would greatly be appreciated.