SQL Query optimization to avoid temporary table

The Table:

CREATE TABLE `T1` (
  `UserId` int(10) unsigned NOT NULL,
  `FriendUserId` int(10) unsigned NOT NULL,
  `IsDisplayed` tinyint(1) unsigned NOT NULL,
  `Created` datetime NOT NULL,
  KEY `FriendUserId` (`FriendUserId`,`IsDisplayed`,`UserId`,`Created`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

The Query:

SELECT `UserId`, `FriendUserId`, UNIX_TIMESTAMP(`Created`) AS `Created`
FROM `T1` WHERE `FriendUserId` = 22
  AND `IsDisplayed` = 0
  GROUP BY `UserId`
  ORDER BY `Created`

EXPLAIN result:

           id: 1
  select_type: SIMPLE
        table: T1
         type: ref
possible_keys: FriendUserId
          key: FriendUserId
      key_len: 5
          ref: const,const
         rows: 1
        Extra: Using where; Using index; Using temporary; Using filesort

Question:

How can I optimize it so that no temporary table is used?