You could specify that it's not for fiction.

That might work, but still obliges subjective (although not quite so heavily subjective) judgment by administrators.

Although even that would be objected to because it cuts out some things.

Specifically, "faan fiction" -- fiction about fandom. (And for anyone else watching, this is not at all like "fan fiction.")

My one paid piece of written fiction (semi-professional because it paid only 1.25 cents/word) was in fact faan fiction -- "The Bridge at Waikiki," part of Again, Alternate Worldcons.