I really like the idea to share a fake list. I think creating separate contact list folders is a bit much for the user, but adding a general permission grant option like "As if empty" or "Use placeholder" might be easier. An app requests my contacts? I can "grant" permission to an empty contacts list.

I think this idea generalizes to other permissions too. Want to know my location? I hit the "placeholder" button and the app gets some generic location that never changes. Valid data flows through, so the app can work, but not my private information.