I know this is an old topic, but I thought I would add my 2p.
Before installing my gauge I read a lot of how to guides which were all helpful but none really explained the best/ easiest route for the silicone hose into the car. I wanted to make sure that I did not have any water ingress into the cabin so set about removing the glove box to get a better look at the bulkhead.
Upon removal I saw an unused grommit which led into the pollen filter bay, I simply drilled a hole in the grommit slid it over the pipe and then reseated into the bulk head. From within the pollen filter bay I then ran the pipe down the plastic cowling that goes into the engine bay (the curved plastic directly behind the airbox) which has a hole I'm the bottom then fed to the FPR.
Sorry I don't have any pictures but I was trying to be quick.
Hope this helps someone.