Thanks a lot for the post! Lots of interesting info!
You can check how it’s done in the source code. Basically, we’re mimicking what site.py does, but we do support an override with IDAPYTHON_VENV_EXECUTABLE so perhaps it can be used in your situation.
The activate_this.py trick is interesting, but seems to be specific to the virtualenv module, while we try to support the built-in venv too, which doesn’t seem to create such a script.