Delayed route loading in Slim

example.php

<?php

require_once 'Slim/Slim.php';

class Custom_Route extends Slim_Route {
    public function dispatch() {
        $this->setCallable(require $this->getCallable());
        return parent::dispatch();
    }   
}

class Custom_Router extends Slim_Router {
    public function map( $pattern, $callable ) { 
        $route = new Custom_Route($pattern, $callable);
        $route->setRouter($this);
        $this->routes[] = $route;
        return $route;
    }   
}

$slim = new Slim;
$slim->router(new Custom_Router());
$slim->get('/', 'example_get.php');
$slim->run();

example_get.php

<?php

return function() {
    echo 'Hello world!';
};