These were the instruction I got from 2k, but they didn't work:
In the folder structure "Users - username - Library - Preferences - Feral Interactive - Borderlands - SaveData", "username" is a placeholder for your actual username.
What I meant was, that you should go to the folder "Users", look for the folder of your actual Username in Mac OS, and once inside, navigate to the folder library, then preferences. In there, please create the folder Feral Interactive, and then the folder Borderlands inside this one, and lastly a SaveData folder inside this Borderlands folder.
Put your files into this SaveData folder, then try again if Borderlands 2 can read your save files.
Does this guy realize I have the steam version of borderlands 2?