Implement a way to minimize full screen windows like games

There is currently no way to minimize or switch away focus from a full screen window like a game.
The standard shortcuts (like Alt+Tab) used by the window manager are ineffective because the X input is grabbed by the application.

Control+Alt+Backspace seems to be caught by the X-server though, regardless of any input grab in effect.
If the window manager could tell the X-server about additional key combinations that should ignore the X input grab, then it would be possible to minimize all kinds of windows using the same keyboard short cut.