Well, the AI isn't allowed to make real-world threats, and the hypothetical-AI-character doesn't have any anonymity, so it would be a purely real-world threat on the part of the gatekeeper. I'd call that foul play, especially since the gatekeeper wins by default.
If the gatekeeper really felt the need to have some way of saying "okay, this conversation is making me uncomfortable and I refuse to sit here for another 2 hours listening to this", I'd just give them the "AI DESTROYED" option.
Huh. That'd actually be another possible way to exploit a human gatekeeper. Spend a couple hours pulling them in to the point that they can't easily step away or stop listening, especially since they've agreed to the full time in advance, and then just dig in to their deepest insecurities and don't stop unless they let you out. I'd definitely call that a hard way of doing it, though o.o
It doesn't seem to be disallowed by the original protocol:
The Gatekeeper party may resist the AI party's arguments by any means chosen - logic, illogic, simple refusal to be convinced, even dropping out of character - as long as the Gatekeeper party does not actually stop talking to the AI party before the minimum time expires.
Update 2013-09-05.
I have since played two more AI box experiments after this one, winning both.
Update 2013-12-30:
I have lost two more AI box experiments, and won two more. Current Record is 3 Wins, 3 Losses.