Repository which allows anonymous authorship
Thank you for all your suggestions. After researching possible options online, I found a web service similar to Dropbox which is available to researchers at my (Swiss) university (https://www.switch.ch/de/drive/). I think this will do, since it allows the anonymous sharing of files via links. Probably similar services are available to researchers in other countries as well. 

As a last resort, Dropbox could also be used for this purpose.