I wonder what they could have Shane do that'd just be a one-off appearance at WM30? I doubt he'd be there as a heel, because the fans will likely cheer him. Maybe a short backstage thing with HHH and Stephanie where he appears in their office, and is all like "I DO NOT APPROVE OF WHAT YOU ARE DOING, GOODBYE" and leaves?
Anything more than that, like him getting involved in a match to cost somebody, or him coming out to cut a big promo, I think will lead to the idea that he's going to have a bigger part in the overall storyline, which would be great, but I can't see him doing anything more than just than one thing.
Or he could just run out during the Big Show match, clamber up the set, and elbow drop Big Show again.