After looking through the projects of Gerben I learned that I can use the tristate input of the uC to mask the unwanted LEDs. Basically it divides the 3.3V voltage in two sub 2.2V that I need to light a LED. It was too much code to use the pinMode function of the Arduino so I put the needed DDRB register values in an array. Now I can do some nice rotating and bouncing effects - wrote some helper functions for them.
So I've updated the Github project files accordingly.