public class MyRadBreadCrumb : RadBreadCrumb
{
    public override string ThemeClassName
    {
        get
        {
            return typeof(RadBreadCrumb).FullName;
        }
    }

    protected override RadBreadCrumbElement CraeteBreadCrumbElement()
    {
        return new MyRadBreadCrumbElement();
    }
}

public class MyRadBreadCrumbElement : RadBreadCrumbElement
{
    protected override Type ThemeEffectiveType
    {
        get
        {
            return typeof(RadBreadCrumbElement);
        }
    }

    public override void BeginEdit()
    {
    }
}