Routing the USB port to the rear of the box isn't very easy. The riser cable for the USB port isn't long enough. Just turning it around to face the rear means twisting the cable... making it difficult to mount.
If there is a size problem, I will just use an L-shaped USB adapter. There is a wide gap on each side of the head unit, as TomatoSoup showed previously.
As to terminating the cable... I'm going to run it through the drivetrain tunnel, under the arm rest. That way, I can use app integration for iHeartRadio, Spotify, TuneIn, etc.
One thing Apple did right was backport iOS app controls to older iPod-compatible head units.