I dont know what u mean with a "better way" if you want to get rid of the stack, just teleport to spawn and come back (this works on factions, should be the same on op). If you want to actually kill them, you can use water as the blazes take damage by it, but this wont make them drop rods or xp and its going to take a while or forever depending on how much spawners u have. Another way is to try to suffucate them pushing blocks into them with a piston, but most of the time they will glitchout from the blocls. Lastly you can just kill em with op weapons, and they will drop xp and rods.