At the time I made this, I had no access to the Big Globe discord server. There is probably a better, updated datapack on there.
This data pack allows YUNG's Better Nether Fortresses to generate in a Big Globe world.
Please note:
Generation can get a little wonky due to the insane height of the nether. I tweaked some parameters to help with this, but fortresses may generate completely buried or have pillars that extend for hundreds of blocks.