As Austria you can keep them in the empire with very little AE. Take Fruili off Venice use this to fab claims on Urbino and the Pope. Release Aquilia, ally Tuscany. Deliberately throw a war to break your vassalisation of Aquilia, ally them afterwards. Now feed the pope to Tuscany and Venice to Aquilia. If you have to (I'm not sure) take Rome for yourself.
As I understand it that won't work. Tuscany and Aquilia won't add provinces to the empire so the event would still fire.