Delphi THTTPRio how to use authenticating proxy server

I've used the WSDL importer with Delphi XE2 and it has generate a routine that looks like the following, excluding the 3 commented lines where I'm attempting to use a proxy server.

function GetIXYZService(UseWSDL: Boolean; Addr: string; HTTPRIO: THTTPRIO): IXYZService;
const
  defWSDL = 'https://server/XYZService.svc?wsdl';
  defURL  = 'https://server/XYZService.svc';
  defSvc  = 'Company.XYZ.Services.XYZService';
  defPrt  = 'BasicHttpBinding_IXYZService';
var
  RIO: THTTPRIO;
begin
  Result := nil;
  if (Addr = '') then
  begin
    if UseWSDL then
      Addr := defWSDL
    else
      Addr := defURL;
  end;
  if HTTPRIO = nil then
    RIO := THTTPRIO.Create(nil)
  else
    RIO := HTTPRIO;
  try
    // RIO.HTTPWebNode.Proxy := 'server_ip:port';
    // RIO.HTTPWebNode.Username := 'username';
    // RIO.HTTPWebNode.Password := 'password';

    Result := (RIO as ISSOService);
    if UseWSDL then
    begin
      RIO.WSDLLocation := Addr;
      RIO.Service := defSvc;
      RIO.Port := defPrt;
    end else
      RIO.URL := Addr;
  finally
    if (Result = nil) and (HTTPRIO = nil) then
      RIO.Free;
  end;
end;

I need to access the service through an authenticating proxy server. I've added the 3 lines shown above and when I uncomment them I cannot connect. The help for THTTPRio states...

If you need to use a proxy server, or if the server requires authentication, use the properties of the THTTPReqResp object that is the value of the HTTPWebNode property to provide the necessary information.

This I have done, but when I attempt to use my service an ESOAPHTTPException is raised having message...

Unauthorized (407) - 'https://server/XYZService.svc'

I've stumbled upon this post that says to set the proxy settings after setting the WSDLLocation, Service, and Port which I've tried with no success.

http://www.delphigroups.info/2/10/555621.html

I am also not building with USE_INDY defined. My service uses SSL so I'm using WinInet.

I am not sure what is wrong with this approach so any help is appreciated.

Thanks, Michael