How to develop another Python process from PYInstaller created by EXE

Question

I am trying to unlock another Python process from a running Python module (ProgramA.pyc) that starts from the pyinstaller exe runtime.

The point is that ProgramA is working fine. However, I cannot program ProgramB to start from the same runtime. I need to emphasize that I need to start and run it (from the ProgramA module), for example:

python ProgramB.pyc. 

I do not want to import ProgramB into ProgramA since its execution, and then blocks the GUI of ProgramA. The ProgramB module is blocking because of the smtplib module that it calls.

Simply running ProgramB.pyc from MEEPASS temp dir is not a solution, since it does not have Python scripts or other available runtime requirements (which otherwise comes from the .exe created by pyinstaller).

In the development environment, I can run ProgramB from ProgramA, and then it really does not block, because it uses a different Python interpreter (all without pyinstaller).

How to do this from an executable created by pyinstaller?

Note: The ProgramB module is located inside the exe created by pyinstaller and is available in the MEIPASS directory. But from the extracted .exe file, it does not get any environment settings.