Parece que se ha conseguido ya el tema online en 5.4
Alright, I got the WUPinstaller working on my 5.4U, and successfully spoofed to 5.5.1.
Host this folder with XAMPP locally (that's what I did, it should work if you have an external server to host it too). And the run it from your browser, should boot you out of browser. Open browser again, visit the url one more time, get booted out, hit Home button on gamepad, and you should receive an error code, but the SD:/install files will have installed. More detailed instructions in the zip.