You could tie them to a table with a hole in it and put a bamboo plant with a sharpened tip beneath. Bamboo grows quickly, and would soon impale them. Plus If you get bored, you could fire a small caliber bullet (So it hurts without being so lethal), dig it out, and then forcefeed them it. Or maybe dump a bucket of boiling water on them, or just nail them to the table and wrap them in razor wire, so they get cut anytime they move... Or just put them in a rubber room filled with rats, they'll go crazy.
