How to add billboards to Mode 7 Shader

Recently, I was asked how to implement a billboard (a static sprite that doesn't move relative to the ground) into my Mode 7 Shader for GameMaker Studio 2. I did implement it before and it's very easy to do, so I quickly threw together this guide on how to:

This simple system is compatible with all camera adjustments, however the size of the billboard sprite, as with the player sprite, will not change. I have yet to find a way to make depth work according to the relative horizontal position of the sprite on-screen. Due to how GameMaker is set up, you cannot simply change the depth of a sprite in the draw event.
Still, I hope this guide is useful to some. I hope you will continue to enjoy Mode 7 Shader for GameMaker Studio 2!