With religious texts and enough surrounding cities with you religion as a majority religion you can sometimes rely on the massive pressure each city exerts on each other to keep a foreign holy city following your religion. This requires you to have enhanced your religion, built Great Mosque of D...., Brodobur, Hagia Sofia before anyone on your continent has founded a religion.Even after they found their relgion the pressure from yours will be too much and you won't have suffered any negative diplo penalties.
I always pick cathedrals for the GWA slot, it seems the AI likes this so tends to use it's faith to purchase cathedrals in all it's cites rather than generate a great prophet. If that happen you might get away with making your religion the world religion on the first WC vote.