CreateXMLInstance for generating wcf message

Is it possible to use the DocumentSpec.CreateXmlInstance(StreamWriter) or a similar mechanism to generate a message instance where no root reference is specified and the schema contains multiple root nodes?  For example, against a WCF generated xsd.

The code below is an example that works against a schema that contains a single root node or a schema that has multiple root nodes with a root reference specified.

public static XmlDocument CreateBTSMessage(string schemaName)
{
            XmlDocument doc = new XmlDocument();
            DocumentSpec docSpec;

            BtsCatalogExplorer catalog = new BtsCatalogExplorer();
            catalog.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings[BTS_CONNECTION_STRING].ConnectionString;

            Schema schema = catalog.Schemas[schemaName];

            Microsoft.BizTalk.
            if (schema != null)
            {
                docSpec = new DocumentSpec(schemaName, schema.BtsAssembly.DisplayName);

                if (docSpec != null)
                {
                    StringBuilder sb = new StringBuilder();
                    StringWriter sw = new StringWriter(sb);

                    try
                    {
                        doc.Load(docSpec.CreateXmlInstance(sw));
                    }
                    finally
                    {
                        sw.Dispose();
                    }
                }
            }

            return doc;
        }