I'm sure there are significantly more accomplished tanks that can address this, but you might also find it helpful after your initial Fast Blade/Savage Blade/Rage of Halone on the primary target to hit your secondary targets with some of these enmity increasing skills in combo as well, in addition to Flash, Shield Lob, and Provoke when necessary.

Also, as the Olyvar mentions, it is in part the healer's responsibility to also keep their enmity in check. It's really a balancing act in a party, and even though it's largely on the tank to maintain control, they can't do it without the help of the healer and dps.