Can I make bolts out of dead goblins?

After slaughtering a bunch of goblin invaders, the dwarfs promptly piled up their corpses in my refuse pile.

Fast-forward a few seasons and the corpses decomposed to the point where only their skeletons remain. Being low on ammunition at the moment I decided to put those goblin bones to good use and make bone bolts out of them, like I sometimes do with cows and kittens.

Trouble is, the dwarfs refuse to make bolts because they need "unrotten bone body parts". But I have more than two dozen skeletons outside!

Can I use those bones or not? If that is possible, how can I get the dwarfs to make nice goblin bone bolts, so they can take out the next wave of besiegers with the goblin's own ancestors?

Have you butchered the skeletons? Dwarf ethics may prevent the butchering of intelligent enemies, but they have no qualms butchering their bones.

Alternatively, skeletons and partial skeletons should "eventually" decompose into stacks of bones. But why wait?