I haven't used cygwin in a very long time, but from I can remember the only way to cleanly uninstall and remove cygwin is to reinstall Windows - because there are parts of cygwin that are not removed during uninstall. Based on that experience, I'm not sure that there is such a thing as a temporary install of cygwin. At least that's my opinion based on personal experience. Perhaps the newer versions of cygwin have a better uninstaller that does completely remove all of it without needing a reinstall of Windows.