Isn't the stocks menu kind of tedious for that anyway? I just d->b->d on the cages' tiles then k->d the cage itself.
Then you just force them to fight your tame macaque army in the arena to the amusement of all.
Wait, wait, what does that do exactly? Dump all of the goblin's items?
... sweet, there's finally a convenient way to deal with goblin captives.
Does it also work if you designate their stuff to be melted?
I take it building a death tower and dropping goblins off it is the most convenient way to free up the cage itself... might as well dump it into the barracks to make absolutely sure they get slaughtered.