There is no need to address ALL the knotty pharasaical arguments used by the Watchtower to defend their blood policy.
Mark got the point Jesus was making in the 7th chapter of Mark.
"Thus he declared all foods clean"
Mark 7:18
So he said to them: "Are you also without perception like them? Are you not aware that NOTHING (that includes blood) from outside that passes into a man can defile him, since it passes, not into his heart, but into his intestines, and it passes out into the sewer? Thus he declared all foods clean."
The new covenant supercedes any other covenant - including the Noachian covenant.
If they want to say that transfusions are "eating" - let them. You can eat blood, you can transfuse blood, you can use it for whatever. The Mosaic Law is finished. Just don't flaunt it in front of someone you know has a weak conscience.