If it's any consolation Fworg64, I was intending to do a similar thing to you. I thought the thing I linked would do it, but it looks like it can't be used for that (I thought you might be able to loop mount it to get the contents of rootfs.img, but that's apparently not possible with ubifs images). It looks like using it as Hoodoo suggested (reflashing the nand with it, copying the nand to a sd card, then reflashing your nand back to hotfix 6a again) is the only to use it directly.
It's a bit of a bummer really, 'cos in my experience the images in openpandora.org/firmware are never exact matches to the nand, so even the one released about the same time as hotfix 5 will have some differences to what nand image + hotfix 5 would be (e.g. libraries missing or added, or older or newer versions of them).