In shadowmoon valley at your faction village (Shadowmoon Village for horde and Windhammer Stronghold for alliance) you may have noticed that there rains down Infernal Attackers all the time. You may also have noticed that the NPCS around them holds aggro on them.
The trick is, remove all your gear but the weapon and auto-hit (auto-shoot) the infernal. You do a minimal amount of damage, thus not getting aggro, but get the same amount ofweapon skill.