From what I understand from skimming some info on the topic, you could tank Leo during one phase with a melee tank without a warlock, but it would be a pita on melee. Plus searing pain means more dmg done to Leo before enrage timer.
Some additional links to supplement bosskillers/wowwiki:
http://elitistjerks.com/f15/t12481-leot ... _question/
http://forums.worldofwarcraft.com/threa ... 6527&sid=1
Leotheras tanking
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