So you're playing a nice efficient game, you know all your dwarves by name and have tasks distributed efficiently, and then you get the dreaded message: migrants have arrived. It's not that we don't want more labor, it's just that it completely wrecks your train of thought, forces you to take time from your devious master plans to figure out what to do with yet another cheese maker and that wood burner with random military skills in towel lashing and basket punching. Wouldn't it be better if you could just toss the noobs into cages and just let them out one by one when you're ready for them?
The trick to getting a dwarf into a cage is you've got to knock him out first. Lacking a trained Cyclops named Bubba to clonk the dwarves on the head, your best option is a controlled cave-in. I've spent the last few hours designing a building that allows repeatable cave-ins while minimizing the chances of damage. (Damage to the building that is - the dwarves come out of it all fucked to hell. Extra practice for your doctors.)
Here it is, the Department of Dwarven Immigration:
RO===O Level 1
|^^^|
D^ ^|
|^^^|
RO===O
+++++ Level 2
+...R
. .O
+...R
+++++
..... Level 3
. .
+++
. .
.....
R is ramps, O is walls, ^ is cage traps, D is door, + is either floor tiles or the top of a wall.
Here's how it works: it's very important that the building face West. Have the dwarf you want to cage deconstruct the floor tile that is the MIDDLE plus (+) symbol on Level 3. (Press d->n.) Because the building faces West he'll stand on the floor tile that is going to fall. He'll fall 2-Z levels and be knocked out, and hopefully land in one of the cage traps in the ring. There's no cage trap underneath him because the falling tile would break it anyway. The connecting tile he's removing doesn't break a cage trap, because it's gone when the cave-in occurs.
The fall has to be 2 levels; a 1-level fall won't knock him out.
To reset the trap, simply reconstruct the two floor tiles on level 3.
It's difficult to do more than one dwarf at a time with this building, because military dwarves stationed on the platform tend to move around and obstruct the tile that needs to be deconstructed. I managed to drop four dwarves at once, three were caged and one landed on the middle tile and was merely injured. I was trying to find out whether it's possible for multiple dwarves to get caught in the same cage if they land on the trap at the same time, but these results are inconclusive (the three landed in separate cages by chance).