- Install Git for Windows SDK somewhere else. You'll need more than 3 GB of free space for that.
- Copy ${git-sdk}/usr/bin/pacman.exe to ${git}/usr/bin
- Copy ${git-sdk}/etc/pacman.conf and ${git-sdk}/etc/pacman.d to ${git}/etc
- Copy ${git-sdk}/var to ${git}/
That's all. You can now open your Git Bash and run pacman -S python to install packages on your existing Git for Windows setup.