This is a big feature request, as our current installer technology is specifically designed for ease of upgrading between minor versions (e.g. 3.6.3->3.6.4). We would need to completely rewrite our installers.

If you want to avoid the installers completely and have partially isolated instances, consider the packages on nuget.org (see https://www.nuget.org/packages?q=publisher%3A%22Python+Software+Foundation%22 ). Note that these may break if you have installed a similar (same x.y) version of Python using the installer, but won't have any trouble if you have used Nuget to install all the versions on your machine.

For fully isolated instances, you can add a "python._pth" file to these after they have been extracted (or a pyvenv.cfg with applocal=1 for Python 3.5). This will suppress all registry lookups that may be confused by normal installs, as well as environment variables and optionally user site packages and .pth files.