I had already forgotten about this thread...
Indeed with minecarts now it is possible to do this.
You require in one single tile to:
1) carve or construct a Track
2) construct a Track Stop and set it to auto-dump in the desired direction
3) make new route and assign a mine-cart
4) set stop 1 to load from the source stockpile
5) make the quantum stockpile a stockpile that accepts the items being dumped there
No need to have two track tiles, no need to have a dwarf guide the mine-cart, basically what happens is that a dwarf takes an item from the source stockpile and puts it in the mine-cart which immediately auto-dumps it.
The quantum stockpile tile can be in the same z-level (no drop chute) and it's perfectly safe.
For an actual drop chute, the auto-dump tile should be a hole, and for safety you need some sort of system that makes sure that no dwarf is allowed access to the quantum stockpile while items are falling down the chute, this can be achieved in many ways...
My system for a safe drop chute involves having the stop auto-dump into a hole, this is the dumping level, so items fall down on the z-level bellow, this level has another hole covered by a hatch or a grate and should be completely sealed by walls, this is the buffer level, the level bellow this is where the actual quantum stockpile is, this is the pick up level, the tile with the quantum stockpile can only be accessed from one entry and after the dwarf enters he can only exit through another path, on his way out he steps on a plate that opens the grate/hatch above and drops whatever has been accumulated in the buffer level onto the actual quantum stockpile on the pick up level.
For instance, dwarf goes to pick up item on the quantum stockpile, to get there he has to go over a closed hatch, after passing the entry hatch he steps on a plate that opens the entry hatch behind him (thus he can not exit through the entry) and opens the closed exit door in front of him, he picks up the item on the QS, then goes over another plate that opens the drop chute to refill the QS, the new items fall from the buffer level on the QS while the dwarf leaves through the open exit door.