It has always been done, by regular users, over the desktop application. The beta group had to create a Linux-usable SD card and go through a process of sorts to load the update onto the Linux card and then proceed from there. Some other folks did it as well, and one of the stickies has the instructions, if I remember correctly.
EDIT: This is the thread
https://www.mobileread.com/forums/sho...d.php?t=111181