I apologize in advance if something similar to this has already been posted.
*applies warpaint*
Ok, first off, set up the below diagram in your fort,
_________________________________________________
X= wall
+= floor
.= empty(channeled space)
W= water (5 to 6 out of seven)
D1= door one
D2= door two
CT= cage trap
FG= floor grate
L= lever
______________________________________
Upper Level
X X X X X
+ + + X X
+ . + X X
X X X X X
Middle Level
X X X X X
X . X X X
D1 CT FG L D2
X X X X X
Lower Level
X W X X X
X W X X X
X W W X X
X W X X X
Ok, after you have finished the above blue print it will require some preparation before we bring the hammerer into this equation. Follow these few steps first:
1. Set D2 as forbidden, it will remain this way until you are ready to reset the trap.
2. Designate the empty space on the upper level as a Pit.
3. Designate the empty space on the middle level as a drinking area.
4. Link the Lever to the FG.
5. Enter the Lever's work profile and disable everyone from using it except the target victim.
6. Check to make sure that the cage trap is loaded.
7. Free the victim's bed.
Once those tasks are completed, give the Lever the pull order and you victim will come running in to pull it. The next step requires micro management, and you may wish to utilize the One-step key. wait until the victim passes over the FG and is in the cagetrap filled space, then forbid D1. All that's left to do now is assign some harmless and optionally injured animals to the pit (Note: using useless cats runs a high risk of failure due to their fairy tale ability of opening forbidden doors) and you're done.
The water will provide drink and the animals will provide food for your target so they don't die.
Enjoy waiting for your caged dwarf!