As I understand it, the ethics around the right to informed consent are with regard to the patient consenting to medical interventions on their behalf, and having the risks and benefits of having such interventions performed on their behalf.
There is no opposite ethical position of "informed refusal". A patient can refuse due to misinformation that they've gathered themselves. They can refuse because they don't like the practitioner. They don't even need a reason to refuse.
Having said that, it would be really helpful to have some kind of resource for medical personnel to utilize when they are discussing blood transfusions with JW patients. Personally, I don't think it would be unethical to include information that raises questions regarding what JWs have been taught, without sounding like undue influence.