I've had great success with amputation by alligator.
It helped that my dorfs were pretty good swimmers. Often the attacked dorf would survive just fine, but his rescuer would be the one who would loose a hand or a foot. I had a dorf with nothing left but one foot, and he became a legendary engraver. He was a hero, having saved... uh... most of many children. We were pretty much constantly producing nice heavy lead crutches, and a named alligator was indeed bludgeoned to death with a rather fancy lead crutch with silver and bone decorations all over it. Sadly the crutch, being a piece of furniture, was not named. Sigh.
Ever since Alligator Creek I tend to only put a dwarf in the position of Champion if they're using a crutch (and thus must be missing part of a leg), and I forbid any wooden crutches, all our crutches are made out of heavy metals. The exceptions to that rule have been particularly spectacular fighters, such as a biting dwarf who killed the enemy with her teeth, and an orphan child I adored...
So why are you trying for multiple amputations? I'm guessing it's not for a crutch toting army if you want three or four amputations. I've found that other than spamming that they can't pick something up, multiple amputees are mostly only good for engraving. What is your purpose for them?