By the way, kinda not related to the current discussion, I just wanted to say that if you have a sig-patched EmuNAND, you can actually convert Loadiine-ready games and apps into SD-installable images through the script I was on about. Same goes for out-of-region titles; I just tested Minecraft Wii U Edition [USA] on my EUR Wii U, and when you edit the <region> property in meta.xml for your own region, you can successfully boot those said out-of-region titles straight from the Home Menu! Pretty cool find.
If any people are interested, here are the <region> values you can change in the meta.xml, depending on your region:
00000002 <-- USA
00000004 <-- EUR
Unsure of the rest, but these are the two most common regions, so...
What would a blank key do exactly? Just not encrypt the file contents? I'm pretty sure the Wii U tries to decrypt the files during installation with its common key, so it might not be able to work.