This is totally done at your own risk but here is what worked for me.
Since this is an update that patches the already installed system I strongly advice against trying this on anything but an non-rooted JOD40D device.
- Download the JOD40D to JDQ39 update.
- Make sure you have ADB up and running. I used this guide.
- Turn off the Nexus 10.
- Start the Nexus 10 while holding down both volume up and down.
- You should get an Android lying on it's back and some device information.
- Press volume down until the left vertical text says "RECOVERY MODE"
- Press power to reboot into recovery mode.
- You'll now get a smaller Android robot, still on it's back, with a red triangle.
- Hold power and press once on volume up to enter the recovery menu.
- Press volume down to select "apply update from ADB"
- Press power once.
- It will now tell you to type "adb sideload <filename>" so connect the Nexus 10 to your computer with the USB cable if you have not already done so.