How to setup a virtualenv withou

First, python and pip themselves have to be installed.

Download virtualenv, setup-tools to a directory, and copy it to internal PC.

pip install --user virtualenv...whl
virtualenv --python=python3 --no-download --extra-search-dir=${VIRTUALENV_INSTALL_PACKAGES}

Now freeze an environment from an external PC, copy them to internal PC

pip freeze > r.txt
#remove pkg-source from r.txt
pip download -d packages -r r.txt

Reconstruct frozen virtualenv

pip install --no-index --find-links=${PACKAGES_DIR} -r r.txt