This cold be accomplished by using a modified version of what I call the "Dwarven Dragonfire Trap-Cannon." Keep in mind that I haven't actually tested this yet...
Here's the original:
M
- ===============================
{=}(g)[ale][ale][ale][ale][ale][ale][ale][ale][ale]
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M = Magma
{=} = Magma-safe floor-grate
== = Walls
[ale] = Alcohol-only stockpile
(g) = Pressure-plate with a goblin standing on it.
The concept works like this: there's a long, one-tile-wide hallway that goblins will be forced to walk down in large numbers, single file. Once the first goblin in line steps onto the pressure plate, magma will begin pouring down the floor-grate in front of him, effectively sealing that entrance to your fortress. But here's the clincher: there is a barrel of ale sitting on top of the floor grate. Once the magma touches the barrel ale of ale sitting on top of the floor grate (also known as the "trigger barrel,") it will predictably burst into flames, igniting every barrel next to it, causing a massive conflagration that extends down the entirety of the hallway; the magma in question harmlessly travels down the magma-safe floor-grate into a magma reservoir, where it can be reused or discarded at your leisure. Because the hallway is one-tile wide, and thus there will not be much room to escape to begin with, coupled with the fact that the hallway is crammed full of goblins, it is essentially guaranteed that every single goblin in the hallway at the time of ignition will be burnt to a crisp, leaving you with all of the Goblinite and none of the mess that comes with flooding an entire hallway with magma.
But you aren't killing goblins; you're killing nobles. Killing nobles en-masse is extremely complicated, and so the dwarffire cannon must be COMPLETELY redesigned.
Here's the redesigned version:
M
- ===============================
{=}(noble)[ale][ale][ale][ale][ale][ale][ale][ale][ale]
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This design is much more complex than the first. Imagine the following: there's a long, one-tile-wide hallway that nobles will be forced to walk down in large numbers, obviously to reach their nobles-only dormitory, single file. Once the first noble in line steps onto the pressure plate, magma will begin pouring down the floor-grate in front of him, effectively sealing that entrance to your fortress. Here's where it gets tricky: there is a barrel of
Elven strawberry wine sitting on top of the floor grate. Once the magma touches the barrel of
ale expensive wine sitting on top of the floor grate (also known as the "trigger barrel,") it will predictably burst into flames, igniting every barrel next to it, causing a massive conflagration that extends down the entirety of the hallway; the magma in question harmlessly travels down the magma-safe floor-grate into a magma reservoir, where it can be reused or discarded at your leisure. Because the hallway is one-tile wide, and thus there will not be much room to escape to begin with, coupled with the fact that the hallway is crammed full of
goblins nobles, it is essentially guaranteed that every single noble in the hallway at the time of ignition will be burnt to a crisp, leaving you with all of the !!Giant cave spider silk sock!! and none of the mess that comes with flooding an entire hallway with magma.