In this miiverse post by Miyamoto, he says that the files can be only accessed on the Wii U browser.
https://miiverse.nin...BAABnUYnWGMmICA
If for some reason you don't want to use the Wii U browser, you can access it on a computer. In order to do this set your browser's user agent to
Mozilla/5.0 (Nintendo WiiU) AppleWebKit/534.52 (KHTML, like Gecko) NX/2.1.0.8.23 NintendoBrowser/1.1.0.7579.EU
If you dont know how, here is a link showing how
http://www.howtogeek...any-extensions/