Now that I have run out of common anode RGB leds I tried to come up with a solution to somehow connect common ground to common anode.
After a few tests I came up with the circuit below. Using 3 pnp transistors it inverts the R-, G- and B- to R+, G+ and B+.
In order to create ground for the led's I connected 3 rectifier diodes to R-, G- and B-.
I am very happy with the results of this circuit and the fact that I don't need an additional wire for ground to drive the common ground leds.
I added the eagle files including the circuit and board. (NOTE: on the board I used BEC PNP transistors)