Wacom Cintiq 24HD Keyboard Holder

No supports needed. Just print.
Optionally you can secure it with a thick 2-sided tape.

Feel free to adjust and modify to suit your needs - i include the flat .svg vector profile for Cintiq 24HD, that can be used as a base for your version.

Have fun!

PS 
(Bolted my keyboard permanently to it, but that is not necessary.)