Find his hammer and dump it. He won't pick up another one.
Not painful enough. I would prefer to have him to at least have phantom limbs.
Besides, dumping hammer seems too much like cheating. Having executioner suffer from an "accident" at the hands of dwarves he tortures seems more realistic
-Easy DF Guide to: HAMMERERS-
1: Lock your Hammerer into a 1x1 room with a spear/spike trap attached to a lever.
2: Pull the lever!
3: Did you get the horribly disfiguring injuries you wanted? If yes, proceed to next step. If not, repeat step 2.
4: Did the Hammerer die from the horribly disfiguring injuries? Start again at step 1 when new Hammer arrives. If the Hammerer did not proceed to step 5.
5: Care for your Hammer in his bed for the rest of his long happy MAGMA FILLED life.
Hmm... What kind of injuries will guarantee him being permanentky bedridden? If he ends up getting better won't he proceed to making a porkchop out of the sentenced dwarves? Can I get him some slash damage that would actually lop limbs off? Will piercing damage froma spear paralyze him?
Also, can I have him alive but horrendously miserable in bed and have him force-fed by my dwarves in such state forever? I was thinking of haivg his "get better" bed in a pond filled with 2/7 water. I can picture him slowly rotting alive on his bed begging dwarves not to shove anymore foor or water down his thorat...