i remember that i did try something, but i don't think that i did find a solution.
but what i wanted to reach at that time was to activate the venv from inside the python scripts that runs in scribus...
i just did a try on linux and starting scribus from a terminal that has the venv activated seems to work correctly.
if you have tried from cmd, you might want to try from a bash shell (as an example the one installed by git...)
maybe somebody who uses windows more often than me can give further advice...
ciao
a.l.e