ok... going from nothing here.
How about an elevator system with a magma water obsidian farm drop room... ambitious I know.
The idea is you have a large drop shaft and several miners on standby. At the top, you cast a 3-z-level high and at least 3x3 dimension rectangular prysm to be dropped down. The migrants or traders enter, drop down, hit bottom, and are dug out. This will require a pump stack, numerous draw bridges, excessive mining, and whatnot.
To get back up you make a tower twice the size and have dwarfs climb it and drop from there.
It is ineffecient, will accomplish next to nothing, and is complete overkill. It will also probably not work. In other words, dwarfy.
Another idea is to have a very high class drowning chamber elevator. You have all dwarfs novice swimmers, and have a tall shaft. At the bottom, pump water in w/ dwarfs inside. As the water rises, to keep above the dwarfs will rise. Eventually they will get to a level with ramps leading out of the water.
and yet another idea, have the same logic work accept going down. The dwarfs get in, the water begins to lower until they have safely reached sever z-levels below themselves. its brilliant.
Build at least one of these. Once you have figured out that they don't work, tell me. Not saying I know they won't work. Just a guess.