[Distutils] custom install directory with bdist_wininst

I'd like to give the user control over where the files get installed. It looks like distutils installs into site-packages by default, and there's no way to override it. The UI shows the destination directory in a box that looks like it should be editable, but it isn't. If you run setup.py install, you can pass a --home that affects where files are installed. I'm looking for something similar on Windows. Jeremy