Clearly the submissions should be implemented via onion routing.
Aaron chooses a path of users from himself to Cyan, picking three fellow users. Call them Alice, Bob, and Eve.
The path is:
Aaron -> Alice -> Bob -> Eve -> Cyan
Aaron encrypts his story using Cyan's public key, then encrypts THAT with Bob's public key, then encrypts THAT with Alice's. At each hop, the receiver of the encrypted story decrypts the message with their private key, and receives the (still mostly encrypted) story, as well as directions as to who to forward it to next. Finally, it gets to Cyan, who decrypts it back to its initial contents with his private key.
* Cyan knows that he received a story from Eve.
* Eve knows she received a story from Bob, and that she is the last in the chain.
* Bob knows that he received a story from Alice, and that he is not the last in the chain.
* Alice knows that she received a story from Aaron, and that she is not the last in the chain.
Easy!
All that effort just to be a dick? I hope you're laughing your ass off.