Actually, the blood/alcohol analogy is correct as far as consuming any substance by needle or by mouth. There's nothing you can say against that specific argument. The only argument against the blood transfusion issue in general, as Saintbertholdt mentioned, is that the blood was only disposed of if the animal was killed for food. If the creature, animal or human, was not killed then it would not apply and blood could be drunk or transfused.
I'm not too comfortable with that argument but it's the only one that may help. A smart JW, however, might counter that argument by asking if it's right to drink human blood even if the person contributing it did not die.
You have to keep in mind that some doctrines in the Bible simply cannot be argued against without arguing against the Bible itself.