I'm not a professional dog trainer by any stretch of imagination, so I was waiting to hear what the pros on here were going to suggest...
But I can tell you how I'd approach this. You'll need a new release word, obviously, and I'd introduce it by marking when the dog looks away. I would start in the down-stay position, just waiting long enough for the dog to look away on his own. Then mark the behavior with the new command and praise/treat/toy while maintaining the down-stay. Eventually the dog will get the meaning. And since you're using a new command, there should be minimal confusion on your current release command.
It's not the size of the dog in the fight, it's the size of the fight in the dog. Mark Twain