Theres no obvious, logical way to do it right now. You'd need a strong heel group to feud with them and (obviously) for everyone to be on the same brand. A lengthy, well booked Roman heel run immediately preceding it (ie ending with him turning face and joining them) might help to bring the fans round to him a little. And a Shield/Bullet Club feud doesnt seem like a bad idea some point down the line if they can build the latter back up as a legit stable again. But this stuff should be at least 2-3 years away because its way too early for a Shield reunion imo.