yes it's possible, it's probably what is explained in stickied threads.
add tubehax DNS to your network settings.
it will block updates, but allows online games if you are on latest firmware version.
if you are not, you have to either spoof (fake) the version so the game think you updated and allows online access, or just update to 5.5.1 and then use Tubehax DNS to block any future updates.
Yes, that's the result I get. But what is tubehax DNS doing different? Afaik, all a DNS Server can do is blocking certain hostnames by not resolving them. So I assume that one of the URLs I am blocking prevents me from playing online - and it's not at all necessary to block this URL, as it doesn't seem to be blocked by tubehax...