Mabye I've got an too old Version of WUPinstaller (I've downloaded the recommended)
Because I've wanted to install my dump of m MK8 and the installer said "Do not try to install games you havn't paid for"
And next to my Wii U is the Mk8 disk ._.
I've tested NexoCube's Wup Installer and it has worked for me. Did you download the file from a (Mega) link posted here: https://gbatemp.net/threads/release-wupinstaller-added-safety.442103/ ?