Saying that the cleric pulls aggro simply due to enemy ai is a faulty argument. The entire concept of an threat based system in a party is controlling what your enemies perceive as a threat, and if that proves to be pointless against an essential part of your group, then may as well do away with the taunt and threat system…
I'd say next likely class is either a druid or ranger, simply to fill the "Nature" skill void outside of kits. I'm hopin' on Ranger and feel it'd be more likely since their skill animations could be easier to design as opposed to a druid's.