How to return the error message to WCF service generated in Message Inspector with Schema Validation

Question

void validateMessage(ref System.ServiceModel.Channels.Message message)
        {
            XmlDocument bodyDoc = new XmlDocument();
            var body = message.GetReaderAtBodyContents();
            bodyDoc.Load(body);

            XmlReaderSettings settings = new XmlReaderSettings();
            settings.Schemas = schemas;
            settings.ValidationType = ValidationType.Schema;
            settings.ValidationEventHandler += new ValidationEventHandler(ValidationCallBack);

            XmlReader reader = XmlReader.Create(new XmlNodeReader(bodyDoc), settings);

            while (reader.Read()) ; // do nothing, just validate
            // Create new message 
            Message newMsg = Message.CreateMessage(message.Version, null,
                new XmlNodeReader(bodyDoc.DocumentElement));
            newMsg.Headers.CopyHeadersFrom(message);
            foreach (string propertyKey in message.Properties.Keys)
                newMsg.Properties.Add(propertyKey, message.Properties[propertyKey]);
            // Close the original message and return new message 
            message.Close();
            message = newMsg;
        }

        private static void ValidationCallBack(object sender, ValidationEventArgs e)
        {
            Console.WriteLine("Validation Error: {0}", e.Message);
            //throw new RequestValidationFault(e.Message);
            throw new FaultException<string>(e.Message);
        }

        object IDispatchMessageInspector.AfterReceiveRequest(ref System.ServiceModel.Channels.Message request, System.ServiceModel.IClientChannel channel, System.ServiceModel.InstanceContext instanceContext)
        {


            try
            {
                validateMessage(ref request);
            }
            catch (FaultException e)
            {
                throw new FaultException<string>(e.Message);
            }
            return null;

        }

The above code screenshot help me validate message requested from client against the schema and throw the errors if some inconsistency happen. But I don't know how to pass error message back to the WCFservice since I also would like to return the error message to the client.

I tried to add the error message to request message and return to WCF service. But I have no idea on how to put the error message to its parent element in the body content which is easy for me to get it in the service operation. Thanks in advance!