Is your battery in the trunk or up front? If it's in the rear then fab up an L shaped bracket and hang it down low under the valance or bumper like what you would see on a typical drag race car. If it's not going to be raced you can mount the bracket so it's tucked up underneath the car a little more.

If your battery is still up front then that leaves you with mounting it near the battery someplace like the fender apron, the frame rail, or maybe down low on the radiator support. If you wanted to hide it you could mount it underneath the battery tray if you have room to get your hand in there to twist the knob.