Install packages without pip

I’m working on developing additions to a Ubuntu-based Thinclient. On this closed platform, I have no ability to use apt, dpkg, pip, … to install packages. In some projects, I came to a situation where I have to add missing python packages to the system. Python (2.7 and 3.8) is available.
The content of the packages will be available on the system.
Is there a way to make them part of the install without using pip?

If they’re pure python (no compilation phase) you can just copy them
into the site-packages area or even better, some directory you just add
to your $PYTHONPATH.

More elaborate packages may require you to run their files.

You could possibly also use “pip install” outside the system, then copy
the resulting tree into your system.

Cameron Simpson