Here is an idea - the tool for the gathering is stationary and activated with heat. When enough heat is gathered the tool is activated and a Revival Fruit is harvested,then the process of resurrecting can begin. If the Fruit process is fine, then Fyrd (or whoever has it for the moment) uses his Drum to summon the spirits of the dead, resurrects them and all are happy.
Some recipe should be invented, in order the Drum (Cauldron item) to work. Just summoning the spirits is too easy for me
In addition, if the heat isn't gathered in time, the Fruit starts to rotten and the revival fails.
Another option when dumping heat in the Tool can be to specifically say who you want to donate for and then if the gathered heat is enough for one of the dead, the Fruit will work only for him/her.
If there is enough heat for all currently dead, I guess it won't be that much of a problem to revive them all with one overcharged and glowing Apple