Working with WCF, given the following operation contract that returns an "Asegurado" object. I want, in returning xml generated, show the item

<a:Asegurado>

<obtenerDatosAseguradoResult ..>

Operation:

<OperationContract()>

Function obtenerDatosCliente(ByVal num As String) As Asegurado

Response:

<obtenerDatosAseguradoResponse xmlns="http://tempuri.org/">

  <obtenerDatosAseguradoResult xmlns:a="http://schemas.datacontract.org/2004/07/dkv.lib.objects.citaOnline" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">

    <a:apellidos>APELLIDOS</a:apellidos>

    <a:fechaNacimiento>1971-03-22T00:00:00</a:fechaNacimiento>

    <a:nif>7777777B</a:nif> ...

How can i achieve this without changing returning object in the OperationContract?