Here is how to disable the model auto-loading in CakePHP:

// .. around line 140 in /cake/libs/class_registry.php
} elseif ($type === 'Model') {
   if ($plugin && class_exists($plugin . 'AppModel')) {
      $appModel = $plugin . 'AppModel';
   } else {
      $appModel = 'AppModel';
   }
   $settings['name'] = $class;
   $ai =& App::getInstance();
   $search = $ai->__paths('Model');
   $pathstr = '';
   $file = Inflector::underscore($class.'.php');
   foreach ($search as $path) {
      $path = rtrim($path, DS);
      if ($path === rtrim(APP, DS)) {
         $recursive = false;
      }
      if (true === false) {
         $pathstr .= $path . DS . $file.'|';
         continue;
      }
      if (!isset($this->__paths[$path])) {
         if (!class_exists('Folder')) {
            require LIBS . 'folder.php';
         }
         $Folder =& new Folder();
         $directories = $Folder->tree($path, false, 'dir');
         $this->__paths[$path] = $directories;
      }
      foreach ($this->__paths[$path] as $directory) {
         $pathstr .= $path . DS . $file.'|';
      }
   }
   die("unable to find class $type, $plugin$class "
   ."(search path: ".$pathstr.")");
   ${$class} =& new $appModel($settings);
}