Custom function to rearrange attachments when creating posts – Almost there

Question

I'm having some trouble with a custom thing I'm doing.

I've implented a custom image uploader into a metabox in a custom post type. Now I'm trying to work out a way that will let me reorder the uploaded images. I found that jQuery Sortable would be a convenient way for the user to be able to just drag and drop in which order the images should appear (in the frontend I'm using a jQuery image slider to show the images and the order of the images are decided by the attachment data "menu_order", so therefor I need some sort of functionality that saves the menu_order that I create with the jQuery Sortable.

Now, this is a simplified example of what I have: http://jsfiddle.net/LN4sA/

Together with each attachment I have added hidden input fields with the attachment id and a field that will house the current position of the attachment in the menu order.

The ID of the attachment is easily fetched with basic WP PHP ($attachment->ID). However, I have not yet found an easy way to populate the #att_order with the proper menu_order. So here I'd like some help/input if someone would be so kind.

To save the actual information I'm using ajax to pull the values from the input fields:

add_action('save_post', 'save_attachment_position');
function save_attachment_position(){
    global $post;
    if ($post->post_type == 'work') { ?>
        <script type="text/javascript">
        //<![CDATA[
            jQuery.ajax({
                type: 'post',
                url: ajaxurl,
                data: {
                    action: 'order_attachment',
                    att_ID: jQuery(this).parents('.attachment').find('#att_id').val(),
                    att_order: jQuery(this).parents('.attachment').find('#att_order').val(),
                    _ajax_nonce: jQuery('#ordernonce').val(),
                    post_type: 'attachment'
                }
            });
        //]]>
    </script><?php 
    }
}

And then use wp_update_post to update the attachment data:

add_action('wp_ajax_order_attachment', 'order_attachment');
function order_attachment($post) {
    $attachmentdata = array();
    $attachmentdata['ID'] = $_POST['att_ID'];
    $attachmentdata['menu_order'] = $_POST['att_order'];
    wp_update_post($attachmentdata);    
}

I'm aware that I need some sort of loop here but I will work that out.

Any ideas?

Thanks