Installing 3rd Python packages not from PyPI


I would like to be able to install some Python packages that are not hosted on PyPI. Usually I do this by simply providing the extra-index-url.
Currently this seems impossible to do for the ScriptEditor, and also to do manually with the Python interpreter.
In an earlier version (either the previous one or the one before) I was able to install my packages using the Python interpreter that I found in .rhinocode, but with the latest version I’m not able to because it appears that the Python runtime is cleared every time you open Rhino and the ScriptEditor.
If I try to install the package and then reset the CPython runtime, I get the issue I mention in Reset CPython runtime doesn’t configure runtime again - Serengeti (Rhino WIP) - McNeel Forum.

This functionality would be incredible helpful for some of our workflows, so I would greatly appreciate it.
Thank you!