You can download an APK using http://apps.evozi.com/apk-downloader/, decompile and modify just as the article has said, and push to the Android SDK's emulator. I have done several analyses of apps using this method and a MITM proxy.

I'm sure there are additional techniques to obfuscate the private key, but relying on locked down devices isn't possible in the Android ecosystem. You don't need a device at all to perform the steps outlined in the article.