I'm not in a position to sugest that you try this, but I've recently seen a very interresting program on TV, where a turtle had been run over by a truck, and was severely injured. The entire back half of his shell was crushed. The vets built for him a lightwieght shell of fiberglass, and attached it with superglue, and sealed it with silicone. The turtle recovered, and did grow a new shell, after which the fiberglass fell off. I was very impressed! Other than this, I'm afraid I don't even know what to sugest, given that you have no way of knowing the extent of his injuries. Bless you for your efforts, and best of luck!