Just install the Theme - Legacy package from Package Control. We aren't directly supporting beta releases, and so I don't think we'll be going out of our way to make it easier to download an old version.
Is there a method which works with the portable version for Windows?
The update_check setting works the same in the portable version for Windows as it does for the regular versions for Windows, Mac and Linux. Note that it is still restricted to only work with licensed builds though.