There is no way! I called Nintendo they told me that if I have no PIN code & no account' password, I have to send them the console.
But the warranty has expired so I'm screwed
Nope there is an EASY fix if your stuck with a PIN . What you need is 3DS Explorer http://3dbrew.org/wiki/3DSExplorer <-- found here. It has an option to unblock 3DS PIN but it also works for Wii U and I'm pretty sure there is a NDS/Wii unlocker too. All you do is enter your Wii U's system date and time,and region and it will generate a master key