I looked into it, and it turns out that I can commit my .whl file to the repository, and then add it to the requirements.txt file. After this I click the Build button

and the .whl file will automatically be installed and used in the pyside project from now on. The .whl file doesn't appear in the file browser for QtCreator, but if I use the terminal, I can add it to the repo. I can't install it using pip in the terminal, because the terminal can't access the venv, that is why I have to use the build button.