Use Calm, instead. Stealing, and Backstab Awareness depends on Line of Site, and Sound. Even Paralyzed, he's capable of knowing you are there, which prevents getting the Backstab Multiplier. I know, he's incapacitated, and helpless, but this isn't Real Life, it's a Game Mechanic. With Calm, they just don't care. Crouch behind them, wait for the Eye to close, and kill him.