Where you add them depends on the process you are trying to create. The obvious place to call this code is when the screen is loaded, in your IW28 flavour itself. To do that, first add the script to a button and test it, then add the button's Object ID as the OnCreateHandler. That will cause it to be called (the button "pressed") each time you navigate to the screen. Once you've done that you can hide the script button as your users don't actually need to press it directly.
As you suggest, you could also add it to the button you use to call IW28. Where your current script stops after navigating to IW28, add a "Refresh Screen" action and then the above code. That should work also.
Steve.