You should be able to show your platform's standard minimize or close button in the taskbar of frame / window containing the keyboard component. Otherwise add an overlapped button or image on top-right of the keyboard and handle its click events. If you prefer it as an actual keyboard key, it might be possible to inherit from the Key class, override its send method with code to minimize when pressed, and add an instance to your custom keyboard layout.

Regards,
Slavcho
Mindfusion