Put them in a specially built 1st layer room/dug out with direct surface access room. Lay the corpses down preferably in line of sight of a enormous bridge door access (which should for the majority of time likely be open assuming there is no risk so hunters/corpse collectors can just dump and waste rubbish there)
Where you put them on the floor does not matter, but if the room has sufficent interior and exterior defenses it helps, as shown on the diagram below the (block = +) roof covers the corpses from the elements and (pillar = P) supports hold up the big roof as well as interior overhang to prevent whatever re-animates or fall into the pit somehow from explicitly crawling out without going up the dirt (walls = w).
In a emergency, drop the pillars to land a killing blow and atom smash them with the bridges/apply traps.
+++++++
P P
W+ +W
WP PW
I like to use this setup for processing hunting in safe biomes (where risk of reanimation is minimal and no necro's exist within distance) and general militia dwarf work in general (running around the map beating up animals on command), its much neater than a stockpile outside your entrance that traders might see or a sloppy subterranean and interior room.
They'll be miasmaless and you can just ignore butcherables/non butcherables. Alternatively i recommend making a dumping hole commode, (a hatch with a lever connected to a deep hole nobody cares about, the smell can't escape so no worries), my bathrooms are terrifying.