OK I sort of did it. I run the cables from the cubby box area, into the hole, behind the passenger seat, underneath the carpet, next to the main loom and left it at that. Happy with that. The next challenge seems to be how to get them into the engine bay area. I used a torch and had a look underneath the T-bar at the grommet through which the main loom goes into the engine bay. It looks as if nothing else can squeeze through this hole, everything is very tight. Now I couldn't see very well but if that is indeed the case, what do people usually do?