"I mentioned the reference to the use of blood from in healing potions to bind them to the intended recipient? I was thinking last night that it reminded me of blood wards. Perhaps it might possible to generalize from the principles used in family wards to allow for the substitution of blood of a relative in cases where the intended recipient is unavailable during brewing, or their blood already contaminated. The first steps towards a general substitution principle might be strengthening the bonding, but I'm worried that might cause the draught to instead react badly to anyone not the blood donor."