I think I can help you out a bit with this one, Rich. Building this application will be a bit different than just accessing a VI. This is because now you are accessing a completely different application. When you are changing a VI, you access LabVIEW through ActiveX. Now you need to access the executable. So, the first thing you will want to do is to register the slave application as an ActiveX server.
Now you can access this ActiveX server. You want to use the three properties Exported VIs, Application Directory, and AppName to build the path to the VI inside the application. From this, you can now obtain a VI reference. Now use this VI reference as you did above to access the VI inside the executable and be able to set the control value.
J.R. Allen