//[HttpPost]
        public ActionResult Update()
        {
            var ymodel = new YourModel();
            UpdateModel<IYourModelUpdate>(ymodel);

            return View("Index", ymodel);
        }
        public ActionResult Index()
        {
            var yourModel = new YourModel
            {
                AlterOnlyInCreate = "only bound in create",
                AlterOnlyInUpdate = "only bound in update",
                PublicValue = "always bound!"
            };

            return View(yourModel);
        }