Interesting that the correct form which co-ordinates someONE with ONEself gets the fewest votes.
I beg to differ. After all, you could replace your 'someone' by 'a person'.
You aren't addressing the person directly. 'Someone as wise as you' can be replaced by 'he'.
"Themselves" and related words have been ever more frequently used as a gender-neutral singular, as "themself" was in Caxton's time.
"you'" is part of the preposition, not the object. The object is "someone," so "himself" is the correct answer.