Another possible alternative is to do a Factory Restore via a file trick, here:
https://www.mobileread.com/forums/sho...d.php?t=223067
If that doesn't work, rsync or something similarly basic should work to copy the firmware update. Make sure you use "--append" so rsync doesn't try to checksum the file first. curl would work too, downloading from a file:/// url.
Just try remembering next time to jailbreak and install Rescue Pack/Cowards Rescue Pack/USBNetwork before you have problems. It helps a lot.