Post a signature from the 5BTC reward wallet, it shouldn't be hard

You can convince me if you also publish the first message "z" in plain text, not only the hash of it...
The only target I see here is the private key of the pubkey:
0337cb099a32bdc5e3b790b0ad94a2c0d1184a1bba7a2b688223a183ff7bdbdf33
...which could be in relation with your real target?!