Trouble with WOWebServiceClient invoke

I'm consuming a WebService written with ASP.net that has a method that 
uses an 'out' parameter, i.e. of this form.

[WebMethod]
int GetResultViaOutParam(out int out_param)

I have no problems if the method has no 'out' parameters, i.e. of the form.

[WebMethod]
int GetResultWith2InParams(int param1, int param2)

The WebObject code for the 'no out params' method is

int arg1 = 3;
int arg2 = 4;
Object[] arguments = { new Integer(arg1), new Integer(arg2) };
String operation = new String("GetResultWith2InParams");
Object res = serviceClient().invoke(serviceName(), operation, arguments);

The WebObject code for the 'out param' method is

int arg1 = 0;
Object[] arguments = { new Integer(arg1) };
String operation = new String("GetResultViaOutParam");
Object res = serviceClient().invoke(serviceName(), operation, arguments);

The exception that is raised by the attempt to invoke 
'WebMethodWithOutParam' is

Error: Error invoking operation: javax.xml.rpc.JAXRPCException: Number 
of parameters passed in (1) does not match the
          number of IN/OUT parameters (0) from the addParameter() calls.

This is the SOAP1.1 response for the service

HTTP/1.1 200 OK
Content-Type: text/xml; charset=utf-8
Content-Length: length

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <GetResultViaOutParamResponse xmlns="http://ipv.com">
      <GetResultViaOutParamResult xmlns="">int</GetResultViaOutParamResult>
      <arg1 xmlns="">int</arg1>
    </GetResultViaOutParamResponse>
  </soap:Body>
</soap:Envelope>


This is the SOAP1.2 response for the service

HTTP/1.1 200 OK
Content-Type: application/soap+xml; charset=utf-8
Content-Length: length

<?xml version="1.0" encoding="utf-8"?>
<soap12:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
xmlns:soap12="http://www.w3.org/2003/05/soap-envelope">
  <soap12:Body>
    <GetResultViaOutParamResponse xmlns="http://ipv.com">
      <GetResultViaOutParamResult xmlns="">int</GetResultViaOutParamResult>
      <arg1 xmlns="">int</arg1>
    </GetResultViaOutParamResponse>
  </soap12:Body>
</soap12:Envelope>

How can I consume the 'GetResultViaOutParam' method?