Yes there is a way but I won't tell yah j/k.
There is a way but if you play a campaign with them you will see that it will be a long and boring campaign because even if you attack catholic factions the won't retaliate and you will be able to rule the word fast and easy... IMO there is nothing gratifying in that.
If you still want to play as them try to go on the TWcenter.com they have alot of things there