...
[Editable(UserName = null)]
public string UserName
...

//модель
public class BaseModel
{
        [Display(Name = "User Name")]                    
        public virtual string UserName { get; set; }
}

public class MyModel1 : BaseModel
{
        [HiddenInput(DisplayValue = false)]        
        public override string UserName
        {
            get
            {
                return base.UserName;
            }
            set
            {
                base.UserName = value;
            }
        }
}

//контроллер
BaseModel m = new MyModel1();            
Return View("MyView", m);

//вьюха
@model BaseModel