Actually, you should be able to.
Go to the harmony app and set up a Smart TV Activity. This is different than a Watch TV activity.
Once you have identified your Smart TV in the harmony app, it should correctly identify the apps in your specific Smart TV.
So, essentially you are building a Smart TV activity very similar to a Watch TV activity. You can then use Alexa voice commands to execute the actions you want.
If this sounds confusing, it's my fault, however try it on the harmony app and it should flow smoothly.