Modifying field behaviour with #submit property

Hi,

I'm attempting to be able to serialize a node, along with any filefield / imagefields attached to the content type. This is similar to node cloning, but the nodes don't really exist. My thinking is this:

1. Enumerate the filefields attached to the node form in hook_form_alter.
2. Add a #submit[] parameter to each field with my own custom function, which takes the uploaded files and stores them appropriately.
3. When the nodes are unserialized, copy the appropriate files from the "cache" and fill in the filefields behind the scenes.

However, I can't seem to get my #submit function to be called. Looking through the filefield code, I don't see an easy way to override how it handles saving a file in some other "CCK-blessed" way.

Here's the snippet of what I'm trying to do:

  $content_type = content_types($node['type']);
  $image_fields = array();
  // Find all the image fields
  foreach ($content_type['fields'] as $data) {
    if ($data['type'] == 'filefield') {
       $file_fields[] = $data['field_name'];
    }
  }
  foreach($file_fields as $key) {
    $form[$key]['#submit'][] = '_skeleton_test_submit';
  }
function _skeleton_test_submit($form, &$form_state) {
  // My submit handler goes here and unsets the field from $form_state when done.
}

Any suggestions? Or am I just asking for filefield to blow up in my face? :)

Thanks!