If I were to go for killing him, I'd do it slowly. First you drug him to sleep (whichever method works best according to situation). Drag his body into an unknown place that YOU have control of. Bind him to a chair and then cut off his feet and hands (making sure he is able to see all of it happening). Then slowly dissect him from the stomach and show his innards to himself until he dies.
Best way to keep him awake would be some adrenaline boosters.