SUF-Z-move lets you arrange the Zwift window to fill the rest of the screen above a The Sufferfest window. SUF-Z-move resizes and moves both windows – The Sufferfest and Zwift – to do so.

If you already know TR-Z-move, this is the same – just for The Sufferfest.
Download and instructions
Go to the SUF-Z-move page for the download and instructions.