Its getting easier to hack your WiiU and the dudes over at wiiubru.com make it a lot easier. All you need is to visit an URL and their code will do the rest.
You need to have the FW v5.5.1 installed and an SD card in order to do it. SD needs to be FAT32 formatted.
The method seems to be simple (i didn't test it). You only have to plug your SD card into the WiiU and visit this address: http://wiiubru.com/go
Click the "Homebrew Appstore" and wait about ~15 to 90 seconds before proceeding. If it takes more than 2 minutes, probably your WiiU has been crashed, so reboot and repeat the process.
From there, you can download the Homebrew Launcher and the apps you wish. You can launch the Homebrew Launcher by visiting this address: http://wiiubru.com/x
For more information, visit this thread.