How can I add additional boards to Eclipse with the Arduino add-on with only a URL, not a zip file I want to add the following boards:

https://redbearlab.github.io/arduino/package_redbearlab_index.json

Which I can add in the Arduino IDE by going to File -> Preferences -> Additional Boards Manager URLs and just pasting it there

Where is the equivalent function in Eclipse, or how do I configure Eclipse to allow me to develop for those boards? 

From Eclipse, I have tried Window-> Properties -> Arduino and from there "Private Library Path" and "Private hardware path", and I have tried pointing them to "C:\Program Files (x86)\Arduino\hardware" and "C:\Program Files (x86)\Arduino\libraries", but that didn't seem to change anything (i.e. no new board options, even after running Eclipse as admin) - while the boards show up (examples and all) in the Arduino IDE
With arduino eclipse plugin 2.4 you simply install the boards with the arduino ide -like you described- and you can use then in the arduino eclipse plugin.

Version 3.0 (that is the nightly as 3.0 still needs to be released) contains it's own boards and library manager in windows->preferences->arduino.