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.

How can I consume the 'GetResultViaOutParam' method?