哈哈，我真的想出了一个办法。作为一个插件，这应该是可行的。

class JPB_CommentCounter {

  var $count = 0;

  function __construct(){
    add_filter( \'pre_comment_content\', array( $this, \'content\' ), 100 );
    add_filter( \'comment_max_links_url\', array( $this, \'counter\' ) );
  }

  function JPB_CommentCounter(){
    $this->__construct();
  }

  function counter( $num, $url ){
    if($this->count < 1)
      return $num;
    elseif( $this->count > $num )
      return 0;
    else
      return $num - $this->count;
  }

  function content( $content ){
    $homeurl = preg_quote( home_url() );
    if( preg_match_all( \'@<a [^>]*href=[\\\'|"](/|\'.$homeurl.\')@i\', $content, $matches ) )
      $this->count = count($matches[0]);
    return $content;
  }

}

$JPBCC = new JPB_CommentCounter();