Evacuate Italy and let those provinces fall into rebellion. That way when the new pope is chosen he won't immediately be at war with you. You definitely need for a pope to be in play in order to launch crusades, but I've yet to see a crusade that really impressed me all that much besides the ones I've launched myself (and properly supported). Sucking troops out of enemies loses some of its luster when you realize what a bunch of genetic throw-backs and losers your AI opponents have working for them.