translucent character

I have a main player character with many materials. What is the correct way to add functionality to make my entire character translucent based on certain game state? (say 0.5f opacity)

I CANNOT modify the materials directly as I regularly get refreshes from the 3D artist.

What is the correct way to programmatically achieve this in C++?

Ask the artist to expose a parameter? Perhaps you could suggest using:

Since there are many materials at play. Your job would be to update one global variable.