Python

I don't think that's possible without some dirty, dirty hacks i.e adding the right paths from the other venv to your running process. Do you want dirty hacks? Because that's just asking for trouble. If you have an application that requires libA-v1 and the gunicorn venv uses libA-v2, you're going to have a conflict at runtime.

I supposes that gunicorn is a shell program ?

source ./bin/activate
which gunicorn # outputs the path to gunicorn
less `which gunicorn` # reads gunicorn

gunicorn takes a module and a module name with a variable name. Modules are found by searching in specific paths. You can add to that search path by modifying PYTHONPATH. How it works is explained here (quite wordy).

To know which path to add to PYTHONPATH, you can either read .bin/activate and figure it out, or run something like bash -c "source ./bin/activate ; env" and it'll list all the environment variables. You can then expand (not replace) the environment variables of the current environment with those of the other environment - either in bash or in python - up to you.

As I said, dirty dirty and honestly I'd just install gunicorn in every venv then you're done with it. But if you really want to, try what I explained and see how it works for you. It's good to experiment and find out first hand.

Anti Commercial-AI license

Why? How many kilobytes of disk space are you going to save from that?