Hi, interesting thread this. I used to have an FZ-10M and always wanted a FZ-20M to have been able to run a hard drive.
Anyway, my point is, If you have a HXC you could use that to transfer disk images onto the hard drive in the FZ of course; but then you "MAY" be able to use the PC app Winimage to take a raw image dump of the filled 512MB FZ formatted card and then re-write that image to another card as a backup. [you can even write to bigger cards but only use up to the 512MB]
It's a shareware app but you will be allowed 30 days to use the full program functions before needing to register. I've been able to image Amiga and Raspberry pi raw card images and then re-write them successfully so with any luck it should work fine on the Casio data. :)
Worth a shot and could save a lot of time & trouble if for any reason the SD card gets corrupted.
Chris.