The quickest way to do this is to start as King Alfonso VI, the King of Leon, in 1066. He starts with a lot of one of the Intrigue Lifestyles completed. The perk you want is Truth is Relative which is the first perk on the schemer path.
Use your sister who will be your spymaster to fabricate a perk on the Pope, this can happen the first time you do it or it can take several attempts. A weak hook wont do it so dont waste your scheme and wait until it offers you a strong one.
Another route is to start out as a different religion which makes it easier to get a strong hook and then switch to the religion of your Head of Faith.