Maybe I searched the wrong terms... has really noone suggested beasts of burden yet?
I mean, all the mules and horses could be put to good use. Instead of taking one piece, a dwarf could round up a mule, take it to several boulders in turn, then lead the mule to the destination pile.
It would be helpful if the beast could be assigned to both work and a cage, so a dwarf doesn't need to hunt it up and down the hallway before the actual work can begin.
As an expansion to the above... I'm lacking the words. How do you call these underground railways? Both the carts and the tracks would need to be made at a metalsmith's, of course. And never mind the tracks, even carts would go a long way.
For loading / unloading puposes, the carts could be treated as yet another stockpile. When it's in the cave, all dwarves round up the rubble and put it on the cart; when it's outside... all dwarves run outside to unload it? Nah, this definitely needs some refinement.
Still, it would be cool if one could actually clear the rubble from the cave with a reasonable amount of work. Right now, the common approach apears to be "make the room twice as large and use half of it as mining pile".