The only way it worked for me was

[Thkoehr]

If you already have an iCloud backup in place, which includes the IOS6 Spotify app, you should reset your iPod, delete all content and configurations and then reinstall the Cloud (!) backup. In my case, it's loading all apps from the cloud ("restoring your purchased content"...) and voilá even the not availlable version of Spotify was back again. I then backed up all apps on this IOS6 iPod on my PC - just in case... You should give it a try!