Without a vet there isn't much you can do for a broken turtle. Generally if the shell has been broken for more than 24 hours then infection has already set it. A broken one needs a vet to flush it, get it on medication & then put that shell back together. Usually they will use an acrylic material made for veterinary use to repair the shell. I have to say after having 1 box turtle & 1 sulcata tortoise (which were both found) repaired correctly by a vet, I've never regretted the money it cost because it worked!
Good luck with this.. if for some reason you can't take it to a vet, have you thought of contacting local vets to get you in touch with a wildlife rehabber?
PHRatz