How do you get proof of car insurance without a car?

I had my brother listed as a driver on my insurance policy and he is moving so will no longer be using my car. The insurance company is requiring that I show proof of insurance before removing him from the policy. They are telling me there is no other way to remove him from the policy due to a DUI charge. Is it even possible to get car insurance without a car? What should I do? I have been in contact again with the insurance company and here is what they wrote back "The only proof we can accept to remove youthful driver's is Proof of Other Insurance." What is the age limit on a youthful driver? My brohter is 24.