Step 1 : Introduce a new mechanic that allows haulers to haul multiple items per trip, based on item weight and hauler strength. Dwarves will only haul items going to the same destination (Workshop, Stockpile, or Tile) from the same source (Workshop, Stockpile, or Tile), so they'll transport a dozen mugs from the workshop to a stockpile, but they won't pick up five different logs to haul back to the fort (Or carry multiple stones, etc etc etc). This does mean that they'd collect 20 seeds from a single chair and dump them all in a bag though, or five different body chunks to the same dump. Hoorah!
Step 2 : SLAVES.
Introduce a new metal item : Manacles.
Squads can carry them into battle. When an enemy falls unconcious they can be captured using Manacles and hauled off to a jail. Also, humanoids captured via cage traps to be taken prisoner and sent to a jail. Even certain megabeasts.
Once in prison, you can attempt to subdue a hostile creature with Manacles. Subdued creatures have a toggle under their preferences : Labor or Imprisoned. When you set them to Labor, they go out and act as a hauler (And work irregardless of any wounds they took while being captured, albeit with the appropriate penalties). When Imprisoned, they rot in a cell.
For an added bonus, allow the subdued creature a low chance* to attempt to escape. Your goblin haulers might try to get free, and in doing so need to be put down by the military. Your captured titan might be an incredible hauler who can cart around time, but when he breaks free he'll wreak havoc until taken down.
* The chance to escape is based on three factors : The manacles strength (Basically their value, since value = Material * Quality which seems a good way to measure strength), the strength of the creature, and the amount of other slaves nearby. An area full of slaves would be more likely to revolt than a creature all by his lonesome.
Lastly, enslaved creatures can be released for all the namby-pamby people who think it's wrong to force goblins or kobolds to act as living wheelbarrows. But hey, if it's good enough for Tropico 2, it's good enough for me!