Creating classes where the return type is dynamic

Ok guys here is the deal. I am working with IBM webservices through Content Manager. Because it is web services I have to compile the WSDL file which then becomes a static document (each one is hard coded per item). My question is some of the classes that help the communictation return a object initialized by this WSDL dll, This becomes a problem if columns are added/deleted or if a new souce is initiated. Because the return type is declared in the DLL how can I make that dynamic so depending on when the itemtype is called the function still works. example problem

Code:

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public test_Bills retrievePolicy(AuthenticationData authData, string pidURI)
        {
            // Create a RetrieveItemRequest to setup the request for retrieving policy
            RetrieveItemRequest request = new RetrieveItemRequest();
            // Set the authentication information for the request
            request.AuthenticationData = authData;
            // we want the metadata and the content as url for the policy
            request.retrieveOption = RetrieveItemRequestRetrieveOption.CONTENT;
            request.contentOption = RetrieveItemRequestContentOption.URL;

            request.Item = new RetrieveItemRequestItem();

            // RetrieveItemRequestItem has a URI field which needs to be set to the PID Uri of the policy we want to retrieve
            request.Item.URI = pidURI;

            // invoke the CM webservice with the RetrieveItem operation
            RetrieveItemReply reply = webservice.RetrieveItem(request);
            // check to see if operation was successful
            if (reply.RequestStatus.success == true)
            {
                // there should be only a single item returned.
                // return the XYZ_InsPolicy object retrieved from the CM server
                return reply.Item.ItemXML.test_Bills;

            }
            else
            {
                Console.WriteLine("Retrieve Policy failed.");
                displayErrorInfo(reply.RequestStatus.ErrorData);
                return null;
            }
        }

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Thanks