Not forgetting that in the top left hand corner of the boot there is a huge access hole which comes out behind the passenger seat behind the small grille.
This is the point that BMW use to run some of the front to rear looms through. I had to use it to retrofit the bluetooth cabling through to the centre console.
BTW - nothing is easy on running cables around the Z4. I've done them all over the place and all are tight and fiddly
Z4 3.0i SE Roadster - ///M front, Red ///M leather seats, Aero sills, AE's, clear lenses, 4 spot rears, custom 108's, paddle shift/MFSW, quad exhaust, 330 brakes, cf rear diffuser, Alutec strut bar, retrofit Bluetooth and a whole host of other subtle mods