Generate new value for _menu_item_object_id ?

I’m working on a plugin which will insert postmeta data describing the attributes set in the Page Parent meta_box during a page creation work cycle. Right now I am hung up trying to track the origin/method used to create an appropriate value for the postmeta field: _menu_item_object_id. Can anyone give me a clue where I would begin to look to resolve this?

public function save_menu_metadata($post_id) {

	if ( 'fixture' != $_POST['post_type'] && 'page' != $_POST['post_type'] ) {
	    return;
	}
	if ( !current_user_can( 'edit_pages', $post_id ) ) {
	    return;
	}

	if (isset($_REQUEST['parent_id'])) {
			update_post_meta($post_id, '_menu_item_type', 'post_type');
	        update_post_meta($post_id, '_menu_item_menu_item_parent', $_REQUEST['parent_id']);
	        update_post_meta($post_id, '_menu_item_object_id', '');	/*	[TODO]  */
	        update_post_meta($post_id, '_menu_item_object', $_REQUEST['post_type']);
	        update_post_meta($post_id, '_menu_item_target', '');
	        update_post_meta($post_id, '_menu_item_classes', array(''));
	        update_post_meta($post_id, '_menu_item_xfn', '');
	        update_post_meta($post_id, '_menu_item_url', '');
        }
}

Any help appreciated.
~ Erik