(Apparently, the link is mod-only, so no surprise I didn't find it before

A short explanation of how it works:
Clicking on the link gets you to a second page which asks you for the anime-name and the episode-number to add the file to. When the anime/ep is found, you'll get to the usual addfile-page, just with the ed2klink pre-entered.)
I can imagine problems with files added that way since the user would most likely not review the other files already listed, but that's something that should be solved elsewhere, for example by adding a list of known files for a certain episode to the addfile-page or warning the user of a file with the same size or group after adding it.