One word: Taunt. If that isn't on his toolbar, it should be. Taunt requires that he be in Defensive Stance (I think), so he can either click the stance bar first or set up a fairly simple macro. Taunt forces the mob to attack him for a few seconds and gives him the same threat as the mob's previous target. At level 61, there shouldn't be any taunt-immune mobs.
Intervene is an ability that will temporarily redirect a single attack without pulling aggro, but I don't know what level it's acquired at.
If he doesn't want to taunt, but wants to pull aggro from the tank through threat generation, liberal use of Heroic Strike and Mocking Blow (in Battle Stance?) may do the trick. However, he has to exceed the threat of the mob's current target by 10% in order to pull. If he wants to play the game this way, have him install a threat meter such as Omen (in fact, all players should get this tool if they ever plan on grouping).
If he wants a comprehensive guide to playing a Warrior, have him delve through the information on .