Removing nether fortress structure while keeping bounding box.

I'm making a skyblock datapack and have gotten stumped on the last structure I need to deal with the nether fortress. I'm trying to figure out how to remove it while still keeping the complex structure box for spawning purposes. I've tried making my own fortress with a processor that replaces all the blocks with air but it doesn't seem to work. If I'm entirely honest I don't know how the fortresses are still generating since all I am referencing is an empty nbt file. any advice appreciated.