you have to participe 10 times in olympiads (it's the minimum to be hero, and I think you must win atleast 1 fight).
Then when you've done your minimum 10 fights, before the hero attribution, switch in the class in wich you don't have your 3rd job/class(p.s: some ppls have the 3rd class skills, but not the name of this 3rd class cause it wasn't established before...).
So in his exemple, at the end you'll compete with the others hierophant but as a PP, if you are the first pp in the list, and if you ask to be hero before the first hierophant does; then you'll be HERO!!!
P.S: GM's wont ban you, cause a lot of peoples are doing this cause the 3rd class quests wasn't established when the 3rd class skills were established.
;) njoy