As an fyi I did try blocking 8.8.8.8 on my firewall and I think that worked, but annoyingly it also broke quite a few of my various Google devices around the house, if I remember correctly. I didn't find a way around it sadly and have up trying.

So I know the answer to this, and you won't like it, on some Amazon fire tablets they have the ability to set two DNs entries, BUT they have a hard coded 3rd you can't remove or change, and that's googles 8.8.8.8, so no matter what DNs you set, route...