XNamespace xsi = "http://www.w3.org/2001/XMLSchema-instance";;
string xml =
@"<Configuration>
  <A type='test'/>
  <B type='test2'/>
  <C type='test3'/>
</Configuration>";

var s = new LiquidTechnologies.XmlObjects.LxSerializer<ConfigurationElm>();
using (StringReader reader = new StringReader(xml))
{
    var o = s.Deserialize(reader);

    // add schema location attribute
    o.UnprocessedAttributes.Add(new XAttribute(xsi + "schemaLocation", "http://server/myschema.xsd";));

    using (StringWriter writer = new StringWriter())
    {
        s.Serialize(writer, o);
        Debug.Write(writer.ToString());
    }
}