All they have to say is that it is now a "conscience matter," acknowledging that some Christians may feel that a total ban on accepting transfusions is required, but that others may feel that the scriptures cited only applied to feeding off unbled animals and doesn't apply under the New Covenant anyway. Different interpretations of what a Christian may or may not be allowed to do were specifically noted and allowed by the Apostle Paul. See Romans 4:5-12.
Note that this same argument could be applied to birthdays, anniversary celebrations, etc, etc. This would be an excellent way for the WT to get rid of some of their most ridiculous rules and regulations. Beards and pants are just the tip of the iceberg.