This is a rewritten post since the way I worded my old post totally confused everyone.
MikeSchinkel shows how he uses Include files in his theme's functions.php file In this Stackexchange post: Organizing Code in your WordPress Theme's functions.php File?
How would you write this php line if the file to include is inside a directory, inside the wp-content directory? Location: [wordpress install]/wp-content/new-directory/my-file.php
The only way I can think of is like this:
require_once( ABSPATH . '/wp-content/new-directory/my-file.php' );
Would this be the correct way?