How to create a semi-transparent ActiveQt window?

I need to create an ActiveQt applications with that is either semi-transparent or has a non-rectangular window shape. This semi-transparent ActiveQt application will be embedded to run inside an external application that might or might not be using Qt.

Request:

• Minimal ActiveQt sample project for a semi-transparent app.
• Demonstrate semi-transparent ActiveQt sample when running in the Qt "testcon.exe" container.

I've already tried to do this myself without success, and then ended up submitting QTBUG-126280 since I was left with the (possible incorrect) impression of facing limitations in the underlying Qt foreign window handling. However, it now seems like the limitation is instead either in ActiveQt or my understanding of how to configure Qt properly.