In order to define a contextual action for spectrum plot windows, you need to put your Python script in your Python directory under a directory called Contextual_Spectrum_Plot_Window.
Go to Tools->Options->Environment->Python Scripts (or Tools->Options->Python->Scripts in INTViewer 5.2) and click "Refresh from Disk". Your script should be listed automatically.
You will now be able to execute this script from the contextual menu of the spectrum plot window:
This script will put this window in a combined window with windows making up the entire selection of spectrum types.
This script is attached to the bottom of this article.
The result after the script executes should look similar to the following.