When you install a module or package using pip in the following manner: pip install --target=<some_python_library_location> <package>
you would expect the package to be installed at the target. If you check-out the documentation, it tells you that that is what happens. It only saves you the typing.
I’m struggling to see why you would want that. You already have separation between the different projects (that is what venv is for) and the separation between different Python versions (comes out of the box). I see only use for the configuration option if you have a constrained system with only 1 Python and you still want to separate the distribution installed library from your own installed packages. It than saves you from the (small) bother of maintaining a virtual environment. Can you elaborate?
I do not install any wheel into the distribution managed environments, so I do not need a workaround to keep these separate from the software supplied by the distribution. Cannot help you there, sorry. Maybe do everything in a venv, instead of (sometimes) still using the distribution installed software?
Your solution will work, but you should never forget to deactivate, otherwise things go wrong. I would prefer a solution which tells pip what to do (e.g. based on a small script in your home directory).