system config tool will also allow it, but I think you might still get a nag mentioning you have too many games when you're on the actual wii u home screen.
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I've never tried playing games through it though. however, I installed almost all my games using it as well as backing up saves (the version I have can't restore them for some reason as the button doesn't even exist). I had no problem with either of those things. I then deleted system config tool, since I no longer needed it.