EventReceiverDefinitionCreationInformation receiver = new EventReceiverDefinitionCreationInformation();
receiver.EventType = EventReceiverType.ItemUpdated;

//Get WCF URL where this message was handled
OperationContext op = OperationContext.Current;
Message msg = op.RequestContext.RequestMessage;

receiver.ReceiverUrl = msg.Headers.To.ToString();
receiver.ReceiverName = RECEIVER_NAME;
//Add the new event receiver to a list in the host web
requestList.EventReceivers.Add(receiver);

ctx.ExecuteQuery();