One option is to build yourself a custom serial cable, and connect it to tx rx pins (that are under the sim card), use 115200 8n1 (non rts) as connection parameters, and do backup from commandline. (enable hardware serialport with flasher --set-rd-flags=serial-console)

Or find someone who can do it for you. ;-).

Downside to this solution is that there are not that many persons in the world that know how to do it. If your located in Finland then you might be in luck, otherwise odds are that much worse.