Extend MENU_LOCAL_TASK of another module

hello there

I'm developing a module which extends another module - node_images to be correct.

Therefore I would like to extend the MENU_LOCAL_TASK which is created by node_images. I want to simply add fieldset.

node_images creates a MENU_LOCAL_TASK

$items['node/%node/images'] = array(
    'title' => 'Images',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('_node_images_edit_page', 1),
    'access callback' => '_node_images_access',
    'access arguments' => array('create', 1),
    'weight' => 2,
    'file' => 'node_images.pages.inc',
    'type' => MENU_LOCAL_TASK,
  );

Now I want to extend this MENU_LOCAL_TASK with a own fieldset.

Do you see what I mean? How can I achieve this?
Is it even possible?

Any advice is greatly appreciated!
thanks!

benjamin