Directly behind the accelerator pedal if I remember correctly... A perfectly designed little entry point for power wire.

 

That gromet is on the left side of the brake pedal. It is actually the stopper for the clutch pedal, if the car is manual you cannot use that grommet.

There is a large grommet in the engine bay that has a lot of wires running through it. Circled in the photo below. You can add a small slit in the grommet using a knife (very small) and run the power wire through there. It will show up behind the dash on the passenger side. If you run it far enough through it will appear cleanly on the passenger floorboard. Thats the way I ran mine.