This is possible! Long story short a comment on YiFan’s 3.2.1 jailbreak page pointed out how to do it. I won’t fully explain how to do it here, but basically you need to use YiFan’s jailbreak, then install usbNetwork access to get SSH access to your kindle. Once that’s done you can copy DuoKan onto the kindle as usual, and use your SSH access to run the install script. I’m new to the kindle jailbreaking world, but everything I needed to download to make this work was available here. Duokan itself (english version) you can get from the links on flip’s post here.
Some notes (mostly to remind myself so I don’t have to figure it all out again next time, but maybe they will be useful to someone)
Jailbreak seemed to work used someone’s perl script to make it quicker
for the usbNetwork portion, I followed the steps in the usbNetwork README_FIRST.txt, only thing I had to do that wasn’t mentioned was set up a static ip for my computer that was in the same subnet as the IP set up on the kindle.
This didn’t seem to be mentioned anywhere in the readme files, but to disable the usbnetworking and get back to disk mode you have to retype ~usbNetwork in the search box.
Original text of the comment from elale.smth on Yifan’s page for posterity:
If you wanna install Duokan (for Chinese user), you need first install usbnetwork-0.33, and copy DK¿s folders to root of Kindle drive. Then telnet/ssh to kindle via usb or wifi to run the following script on your kindle:sh /mnt/us/DK_System/install/install.sh(this is just the installation script of Duokan, which cannot be executed by its update bin file, so you need to do it manually. Now you can ¿reboot¿ your kindle to make it work).