Modifying RSS item

Hi

I created a small "digg this"-like module that inserts a widget in the beginning of every node in the following manner:

function dzone_nodeapi(&$node, $op, $a3 = NULL, $a4 = NULL) {
  if ($op == 'view' ) {
    //Check our node is one of the ok types
    if(in_array($node->type, variable_get('dzone_node_types', array()), TRUE)) {
      $node->content['dzone_button'] = array(
        '#value' => theme('dzone_button', $node),
        '#weight' => variable_get('dzone_button_weight', 10)
      );
    }
  }
}

Unfortunately I can't understand how to add the same stuff to the content pushed to RSS feed. I tried playing with $op=='rss item', but so far managed to modify only item title, not the item body.

Could you, please, advise how to add text to the RSS item body?