I was wrong, it still works
1. Pull the APKs of your Android phone
Connect your Android phone with USB debugging enabled.
Get the package name of Spotify:
> adb shell pm list packages | grep spotify
Get the file location of the APK:
> adb shell pm path com.spotify.music
Pull all the files to your computer:
adb pull /data/app/com.spotify.music-PrDoHptneXuzOEGlVbRlqg==/base.apk spotify.base.apk
adb pull /data/app/com.spotify.music-PrDoHptneXuzOEGlVbRlqg==/split_config.armeabi_v7a.apk spotify.split_config.armeabi_v7a.apk
adb pull /data/app/com.spotify.music-PrDoHptneXuzOEGlVbRlqg==/split_config.de.apk spotify.split_config.de.apk
adb pull /data/app/com.spotify.music-PrDoHptneXuzOEGlVbRlqg==/split_config.xxhdpi.apk spotify.split_config.xxhdpi.apk
2. Push the APK files to the UT phone
Now disconnect your Android phone and connect your UT phone with USB debugging enabled.
Push the files to the phone:
adb push spotify* /home/phablet/Downloads
3. Install the APK files on the UT phone
While the UT phone is still connected via USB, first open a shell on the phone:
Next commands are executed on the phone!
adb install-multiple -p spotify*
Unfortunately the new app drawer (which has replaced the old app scope) doesn't refresh and I don't know how to refresh the installed app icons manually.
So it seems you have to reboot the UT phone before you can tap on the Spotify icon and start listening to music.