If anyone has any info, please share.
According to the initramfs from the 5Big kernel, it uses the same way to recognize a unitialized hd as other Lacie raid devices. The string "LaCieFirstBootLaCie" at offset 1536. There is a script inside which contains this code to write it:
echo -n "LaCieFirstBootLaCie" | dd if=/dev/stdin of=$l_device bs=1 seek=1536 count=20
You could try this on an empty disk, to see if the NAS accepts it. If not, you can lowlevel copy a current disk, and then write the first boot signature.
(BTW, this string is on boot exchanged by "Lacie5Big" or something like that)