Hacking Blocking Wii U system updates by URL blacklist, possible?

[Helsionium]

OK, blocking the URL given in the second post did not prevent the system update from downloading.
But at least I can confirm that you can enter vWii mode even when a system update is available, even while downloading and when the download is complete.
However, once the download is complete, you must install the update the next time you (re)start the console. I didn't try the vWii shortcut (hold B while booting) at this point, but I guess it won't work - maybe someone can confirm.