First, let me preface my suggestion with the statement that I know nothing about frostbite. However, I have a real hard time with "there's nothing you can do" so I will always try something (no matter what the case/condition). In this case, I would spend a lot of time gently massaging his ears. Maybe, just maybe, they aren't so far gone that you can't get some nice warm circulation going to the tips of his ears and, if so, they won't die and fall off. Again, just my humble suggestion that when feeling helpless, try something/anything - AND - PRAY.
The Lord has healed many of my pets - including our cat Morris who was given less than 5% chance of survival by our vet when I ran over Morris severing his spinal cord near the tail. Morris went home the next day and is alive and well. Though his tail hangs down - the tail did not die and he has full use of bowels/urine which vet said "would never happen even he survived". He walks, talks, runs, jumps just like he did before the accident. He doesn't, however, sleep under the car tire anymore.