Depending on the trim level of your car there aer a couple of spots that are Ideal to run heavy guage power wires through from a reloacted battery. In my setup I actaully used EMI shielded, sliver plated expensive ****, and ran it through the gromet that all the ECU wired com in through. All it takes is a small cut on the way though the gromet, becareful not to knick your wiring haness.
Or if your car without a/c, you could use the hole the the a/c lines normally come through. You'll prolly have to drill or cut a hole in the plastic/rubber block-off plate.

~Steven