I can’t speak for the team but my understanding is that it is not doable due to security concerns.
And yes, you can achieve this in a self hosted instance. You will need to build the package first before deploying the docker image, and ensure to add the pypi instance there, before spinning up the docker container.
More information can be found here on how to deploy a custom python environment. I believe you will need to change it to include your pypi instance in the dockerfile instead since now python is already packaged in the normal n8n build.