After struggling looong time, and getting a lot of damage to my hands, I came across a way to get the dock unit to fit in the radio slot of the car.
Problem is, that the aircon is fitted just behind the radio slot, leaving very little space for all the wires, that comes with the dock, and I never wanted just to push it in using force. After a while, I realized, that I had to get my hands in behing the radio while pushing the dock in, and pull/arrange the wires as they came in. So which way to get in? Studying the interior a bit revealed, that the ventilation outlet at the top of the dash, also allows you to access the back/side of the radio slot, and vupti, nicely mounted suddenly, wires arranged, pressing the mount tabs, and an even happyer empeg owner.