How about a stipulation we haven't seen yet this year? No ladder, steel cage, last man standing or even hell in a cell, since we're getting that anyway in October.
Maybe a 2 out of three falls match. I know we got that between Miz and Caesro in March but that was on Smackdown, not PPV. Or just do another regular match, with the stip being that everyone is banned from ringside. Maybe also add in a stipulation that says that Del Rio can lose the title by count out or disqualification. Ziggler could request that this stip be added to the match just to make sure there is no dirty way for Del Rio to slip out of in any way, shape or form this time. He really will have to pin Ziggler or make him submit in the middle of the ring to defeat him and retain the title.