As far as including the origin, Denny O'Neil used to have this great way of including a small mention of it in a panel or two every so often; not enough so that you'd get tired of it, but enough to (a) give new readers a quick refresher and (b) remind readers that yeah, this is what happened, it's basically his raison d'etre but we're not going to dwell on it. Seems to me like the cinematic equivalent, whatever that might be, is the way to go.