Add option to disable copybox in teaser display

Without this feature, I can't use the copybox option... I fix it with this hack:
if ( $a4 && variable_get('permalink_display_node_copybox_'. $node->type, FALSE)) {

/**
 * Implementation of hook_nodeapi().
 */
function permalink_nodeapi(&$node, $op, $a3 = NULL, $a4 = NULL) {
  switch ($op) {

    case 'view':
      // If this node type is set to display a copybox
  
      //if (variable_get('permalink_display_node_copybox_'. $node->type, FALSE)) {
      if ( $a4 && variable_get('permalink_display_node_copybox_'. $node->type, FALSE)) {
        $node->content['permalink'] = array(
          '#value' => theme('permalink_copybox', $node),
          '#weight' => 51,
        );
      }
      
      break;

  }
}