Rabbits generally handle the cold well; it's the heat you've got to worry about. None of my English Lops have ever had trouble with the cold and their ears; then again, mine are kept in the garage and it rarely gets below freezing.
There's really nothing to put over their ears to keep them warm (I know my bunnies would have a blast ripping off "ear socks" and chewing them up lol), but if you're worried about the cold, you can stuff their hutches full of hay to provide some warmth and insulation, and make sure the hutches are protected from the elements- This means making the hutches well built so that there's no drafts or leaking, covering them with tarps if the weather is really bad, making sure they're sturdy enough to handle a build up on snow on them, etc.
Make sure you use water bottles instead of crocks; English Lops can dip their ears in the crocks, and the water can freeze on the ear.
Holly