public class MyCustomViewModel
    {
        public int Id { get; set; }
        public DateTimeOffset Created { get; set; }
        public string Title { get; set; }
        public int SomeNumber { get; set; }
    }

@model MyCustomViewModel
@{
    ViewData.TemplateInfo.HtmlFieldPrefix = "Custom[" + Model.Id + "]";
}

@using (Html.BeginForm())
{
    ........
}

    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum 
     | AttributeTargets.Interface | AttributeTargets.Parameter, AllowMultiple = false, Inherited = false)]
    public class RoutePrefixModelBindAttribute : CustomModelBinderAttribute
    {
        public string Prefix { get; set; }

        public string Parameter { get; set; }

        public RoutePrefixModelBindAttribute(string prefix, string parameter)
        {
            Prefix = prefix;
            Parameter = parameter;
        }

        public override IModelBinder GetBinder()
        {
            return new RoutePrefixModelBinder(Prefix, Parameter);
        }
    }

    public class RoutePrefixModelBinder : DefaultModelBinder
    {
        private readonly string _prefix;
        private readonly string _parameter;

        public RoutePrefixModelBinder(string prefix, string parameter)
        {
            _prefix = prefix;
            _parameter = parameter;
        }

        public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
        {
            var paramValue = bindingContext.ValueProvider.GetValue(_parameter).RawValue.ToString();
            bindingContext.ModelName = _prefix + "[" + paramValue + "]";
            return base.BindModel(controllerContext, bindingContext);
        }
    }

        [Route("some/{id}/edit"), HttpPost]
        public ActionResult Edit(int id, [RoutePrefixModelBind("Custom", "id")] MyCustomViewModel model)
        {
            if (ModelState.IsValid)
            {
               ...
            }
            return PartialView(model);
        }