Have the Ottomans invade Italy and take Rome.When the Papacy starts considering where it wants to relocate to Avignon will look promising as A) They already own it B) It has previously been the Papal residence and C) France being both strong and on relatively good terms with the Ottomans is unlikely to be invaded by them. Even if the Ottomans lose Italy after 2-4 centuries the Papacy stays put as there is little reason to move back to a redeveloped and Ottomanized city whose new rulers may or may not be friendly.