Slightly less hacky: check the path from python -m site --user-site then create that dir then in that create usercustomize.py that tries to import onnxruntime (except: pass). And then set an envvar ENABLE_USER_SITE=1 whenever you want to trigger that. This will always try to import that module in any env before running your own code.
@Otakuwu you need to pip install what you yourself use (typically: whatever you directly import). Your dependencies are responsible for pulling in their own dependencies.
@Otakuwu python -m venv venv_name creates a venv called venv_name, then . venv_name/bin/activate or on Windows venv_name\Scripts\activate or something like that activates it, then from then on python belongs to that venv