This how I did it. I do not use this car and the GPS daily so I was looking for a solution to use my TOMTOM XXL in my X1 without any visible wires and when the GPS removed no signs of a GPS system in this car ever used.
I bought a cradle for the TOMTOM XXL from Brodit, had a 12 V wire installed in the compartment. When you put the GPS system in the cradle you can clip it between the cover of the compartment and the rubber inlay. It really fits well.
The pictures will show it.