That won't really work. You could in theory run a game in fixed window mode and use a controller only, that may work if the game doesn't depend on having "focus".
You see, when you click off screen during a fullscreen game - the fullscreen game will minimize. Fixed window mode takes care of this. But fixed window mode is basically just a window, and as you know, you can only type/click on the window that has focus. As soon as you click a word document, his game will lose focus and his inputs will be sent to your word document, and vice versa.
Sound is also a problem. There is no native option to have separate sound sources outputted from a single audio device in your PC. There are software solutions but i haven't found one i...