The thing is, mechanics influence behavior of players to create genre adherence. If you want folks to act like mythos sorcerers, reward them for it and guide them that way using the mechanisms of play.
I think that the plan would have to be making sanity points very tempting to spend, as a wizard. Perhaps, like luck for a halfling in DCC, sanity does -more- for a wizard. It is a sacrifice they have learned to master.