Sorry for the delay jonny, here is the pic which apparently shows how BMW secured the tube onto the bumper.
When i took my bumper off, i discovered that the flexible intake hose wasn't secured properly. I think most BMW dealerships don't know how its mounted properly, so they just stuff the tubes behind the bumper and et
voilĂ*.
Anyway, here is the pic i've found somewhere long time ago.
Flexible Tube is held by 2 push pins onto the Bumper itself and the large zip tie prevents the flexible tube from resting on the fixed tube below.
Good Luck, if you have any questions just let me know.
I promise i'll be faster this time