I'd also go with fresnel.
Since the fall-off shader takes the whole object into account, everything after 50% of the gradient won't be visible since it's going to be projected onto the objects back-side.(z-camera view)
However, it might be useful for non-opaque materials.
Edit: Since we're already on the topic of fancy materials, what about the thin-film shader?
I know it's mainly used for coatings, oil, iridescent mats etc. But could it play a role in this? Could it be abused instead of the fresnel shader to take the job?(given the right values&expressions)