Hello,
this is not possible.
The WiiU deletes the Partition table (located on sector 0 of the HDD) so you can't store multiple partitions.
it uses its own raw encrypted format starting at sector 0.
That's the reason Ustealth hides the entire HDD and not partitions.
the only way to achieve what you want to do is very very very hard, and not usable. (hint: by faking the size of the HDD to make a shorter wiiu partition, and storing a backup GPT partition table at the end of the hdd), but nobody tried that. it's only theoretical, and needs so much steps to setup, and no homebrew compatible with end of HDD's table make that idea useless. Even less when homebrew expect MBR instead of GPT.
you can read the Ustealth thread, that idea is in there.
