The addon circuit fuse holder can normally be bought at car accessory shops.
Sorry about my last reply. It was not really to do with this thread.The addon circuit fuse holder can normally be bought at car accessory shops. That photo i have shown is the addon unit piggybacked onto the 15 amp fuse. You can use it in any of the unused slots next to that 15amp one as they are all switched live power. This is on the mk5 fusebox but i don;t expect the mk6 to be any different.
Sorry not a direct answer but I used tomtom on a navman on Saturday and the unit fitted perfectly in the space with the ashtray and all the wires tucked in behind it. I'm not sure what size your TomTom is but having it down there beats all those trailing wires.