As far as I know, there is no other option so far. According to customer feedback, it should work with the German account.

In principle, a German address is not necessary for Alexa. However, external services such as Spotify can only be paired if a German address is stored.
With Bose, a location check comes into play during the setup. The app recognises like IP whether you are in Germany or not. Since this is ONLY done during setup, you can change your location with a VPN service. And then you can select and link the Alexa voice service.
You still need the "Bose" skill from Alexa. You can set this up via the website or app (only available with the German store).