Call Default Model Binder from a Custom Model Binder?

Derive from DefaultModelBinder and then invoke the base method:

public class DateTimeModelBinder : DefaultModelBinder
{
    public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        // ... Your code here

        return base.BindModel(controllerContext, bindingContext);
    }

}

Well, it is actually a trivial solution: I create a new instance of the default binder and pass the task to him:

public class DateTimeModelBinder : IModelBinder
{

#region IModelBinder Members
public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{

    if (controllerContext.HttpContext.Request.HttpMethod == "GET")
    {
        string theDate = controllerContext.HttpContext.Request.Form[bindingContext.ModelName];
        DateTime dt = new DateTime();
        bool success = DateTime.TryParse(theDate, System.Globalization.CultureInfo.CurrentUICulture, System.Globalization.DateTimeStyles.None, out dt);
        if (success)
        {
            return dt;
        }
        else
        {
            return null;
        }
    }

    DefaultModelBinder binder = new DefaultModelBinder();
    return binder.BindModel(controllerContext, bindingContext);

}
#endregion
}