I still don't think it is. Look at his face in the run up to the scream. He ain't happy. He'd just had his ship attacked and heavily damaged with loss of life, found a load of bloody corpses with their throat cut, his ex and child were missing possibly dead, just witnessed a fellow officer commit suicide and one of his close colleagues had collapsed and an alien creature bloodily emerge from his ear, his estranged son had just attacked him with a knife, and his greatest enemy had just stolen a domesday device, and was taunting him about it.
Regardless of what he had up his sleeve (and there was no guarantee it would work) Khan had the upper hand and at the moment of the scream, he had every reason to lose his shit. The only subterfuge I got from the chain of events was that he didn't tell the rest of his crew, only Spock was in on it, which when you think about it is a bit out of order considering what everyone was going through. It wouldn't have hurt Kirk to disclose his plan to the rest of them considering they were contemplating being trapped there indefinitely.