How do you keep a Billboard GUI's size when zooming away from it?

It is not possible to keep the same size of the billboard gui. As you can see in many other games when you open a billboard gui from the player's torso, it grows in size as you move away. The size of the gui is not changing, it just visually changes relating to the parts of your character/your camera. I am sorry you are not able to do this but, it is impossible.