This script will create a Spectrum Plot Layer when you create a Spectrum Layer by drawing an Analysis Rectangle.
Put this script in the On_XSection_Analysis_Rectangle_Created in your Python scripts directory.
Go to Tools->Options->Environment->Python Scripts and click "Refresh from Disk". Your script should be listed automatically.
Now, whenever you draw an Analysis Rectangle to create a Spectrum Layer, a Spectrum Plot Layer will be created.
This simple script is useful for creating multiple windows from drawing only one Analysis Rectangle.