It's fairly easy to get a secondary passport (Zweitpass) in Germany. You need to give them a good reason, and they are very likely to request something in writing (from your employer/school/some fancy letterhead you printed on your cool new laser color printer). I doubt that the whole Cuban/US etc argument would impress a skilled Einwohnermeldeamt bureaucrat, but I've used the following for over a decade: I live abroad and need to have my (main) passport with me at all times. While abroad, I also need to apply for visas for other countries, so I need to send my (second) passport away. If I only had one passport I would violate the laws/ID requirements of the country I live in, hence I need a second passport. Never had any problems with this argument, and it worked well for countless friends/colleagues.