I would torture him! Firstly, i get some Hot Sauce, squeeze it all down his throat... Get a hamster, shove it up his butt, get a knife and repeatedly stab him... Let him lie there for a few days... Come back and feed him and give him water, Patch up his wounds, and then repeatedly shoot him with an Airsoft Gun. Then repeatedly stab him with knife again... Rinse and repeat until i get bored.
1. I tie him to wooden pole. 2. I get a giant sword and stab him for 3 minutes. 3. Leave him there for the next 2 hours. 4. Shoot him with a Desert Eagle in the shoulder. 5. Paint "Sporex was here" on his body. 6. Skin him alive. 7. Run over him with a steamroller. 8. Fart on him. 9. Bury him.
Tough decision, it is actually a question of "can he fight back?" if so then I would do a quick treetop assassination or treetop spinal injury causing him to be able to be tortured but if he was incapacitated I would torture him slowly while my pet chews his legs off