I was waiting for @aparker to comment but I believe this is the prefered way to install the standards gem. Basically you install it in a user location and then set GEM_PATH (which is separate from RUBY_PATH) to this location. The gem will be loaded from your user location before any other location:

1. Check out https://github.com/NREL/openstudio-standards
2. cd \openstudio-standards\openstudio-standards
3. bundle install
4. rake build
5. gem install --user-install pkg/openstudio-standards-0.1.0.gem
6. Set environment variable GEM_PATH to the user gem directory, e.g. C:\Users\dmacumbe.gem\ruby\2.0.0