Once again, I repeat, that this may be simplified using the forbidden barracks system. You set up a barracks like so...
WWW
WAW
WDW
WHW
WDW
W W
(W)all, (A)rmor stand, (H)atch, (D)oor
The upper door is set to internal forbidden, the bottom door is normal. When you create a barracks here, it will result in a 1x1 room that the dwarves can be in, and they'll pack themselves like sardines into this one square, eagerly awaiting/dreading the pull of a lever. Or, more creatively, the tap of a pressure plate. If you set their drop zone like so...
+++++
+BBB+
+BPB+
+BBB+
+++++
(+)Floor, (B)ridge, (P)late
with the bridges channeled out with no ramps underneath. This would make a 1x1 floating island of sorts, which should be set to trigger when a goblin steps on it. Thus, the goblins will walk in and one of them will hit the pressure plate. Immediately, the bridges will disappear (use retracting, not drawbridges) so that the lone goblin is stuck on that tile, while any neighboring goblins fall below. Since the pressure plate is ALSO linked to the hatch 30 levels above, it will cause your troops to fall out, landing safely on the goblin, where they proceed to butcher the poor greenback. Once dead, the pressure plate will deactivate, making the bridges re-appear and allowing your soldiers to rush out and kill the others.
This is, by no small stretch of the imagination, a self-reloading, self-sustaining orbital drop system. You simply order your solders to train in the barracks, and they group there, being automatically launched when needed. Because of this, you don't even have to order your soldiers to kill! Just have them training year-round, and they'll naturally train, slaughter when needed, and walk back up to the drop pod all on their own!