The KM windows are different from most, and are not readily detectable by normal means. Take a look at this macro by @Tom:
Macro: Manipulate KM"s Display Text Window
You will need to change this line in the script:
tell window "Keyboard Maestro - Display Text"
to be the name of the Clipboard Switcher.
My first guess would be: "Clipboard History Switcher"
Good luck and let us know how it goes.