I checked through the diplomacy and mission text files there is a faction mission called Regicide. The mission is to assassinate the faction leader. I have received this mission once while playing. In that case it was to assassinate the faction leader of an allied faction. There is also a council of nobles mission to assassinate a general. There is a line in that mission commented out:

; character_type named_character

I would think that you could add another mission and set the conditions so you don't get some dip as an heir.