If you don't mind running a water system, could you use running water to wash the bodies from the kill floor into a repository or something with an atom smasher? Just a thought.
I've only seen living and reanimated beings affected by moving water.
You obviously haven't played on an ocean embark trying to recover stuff moved around by the surf... (I once made the mistake of deconstructing the embark wagon that stood in the surf area, and the cancellation spam resulting from that has made an impression).
This bears a little more complete explanation, because building systems to flush items via water flow is possible, but very difficult due to limitations in the way flow is implemented.
Wiki article on water flowThere are two ways liquids can move, teleportation (water pressure), and "flow" (my word choice) when water moves downward or sideways to an adjacent tile with a lower level of water. That flow is what can move creatures or items, and only exactly one tile at a time. Pressurized water (like a long pipe full of water fed by a large cistern above) looks like it's flowing, because water is streaming out the end, but the tiles in the pipe are not aware of any water movement, because the water is actually teleporting from the top of the cistern to the end of the pipe.
Item movement is possible, e.g. if you have three tiles horizontally and dump/pump 7 units of water on the leftmost one, you might see a sequence of water levels like:
700
610 (items in the left tile might move to the center tile)
520 (items in the left tile might move to the center tile)
511 (items in the center tile might move to the right tile)
421 (items in the left tile might move to the center tile)
Since there are only 8 possible amounts of water on a tile (0-7), it can be complicated to set up a reliable, directional gradient of water levels that will move items somewhere more convenient. As the system empties, some backwards motion is almost unavoidable in horizontal sections, since you'll see water level patterns like 121 at some point, where the 2 can move left or right at random, and is likely to bounce around between the three positions until it flows away or one of the 1's evaporates.
If you ever fill the entire area up with 7/7 of water, item movement won't happen until some of it starts draining.
For me, this usually means that the item transport distance is limited to a few tiles, maybe from a trap hallway through a row fortifications directly adjacent to the hallway.
None of that really solves the psychological problems, since you still have a pile of FPS-damaging invader bits to deal with, only one hallway over. I'm glad Toady circled back to make psychology matter again, but it could use some more thought on the details of the mechanic.
I encourage trying magma as a solution, just for the Fun of such an exercise, though!