With some renovation I decided to wire the beamer in a more stylish way.
So I took the Landmark of Kronach (region Oberfranken^1, Germany) "Festung Rosenberg" and designed from it's contour this cable canal. You mount it on the wall with nails (take a spirit level ;)) and then push the cable in it. From one side electrical wire, from the other video signal. Be sure to have cables which are long enough. If you look closer, you will notice the VGA-cable (5m!!!), which is too short. But this beamer will be replaced soon and then I will get HDMI.
Maybe you don't want to have the Festung Rosenberg in your living room - maybe you will take it as an example and create your personal/historicol/cultural ... thing. Have fun!
^1 The people here are very aware of their area. It's located in the north of bavaria, but in general conciousness it doesn't belong to bavaria.