Replace a method in a global object. Not working yet. Just a concept that I discovered I didn't actually need.

better-broken-class.php

class Better_Broken_Class extends Broken_Class {
	private $parent = null;

	function __construct ( $parent ) {
		$this->parent = $parent;
	}

	function __call ( $name, $arguments ) {
		if ( 'function_to_replace' === $name ) {
			// do other stuff and return
		}

		call_user_func_array( array( $this->parent, $name ), $arguments );
	}
}
global $broken_object;
$broken_object = new Better_Broken_Class( $broken_object );