i did it like this :
just make wooden floors stick to the nest until stop auto spawning in this way ( there some buildings that make with some distance but floors helps more for this thing ) , when the nest stops , make the floors cover the area you want , when you finish , start diging underground the floor but whith poles to not make them fall , when you dig the pit you want , destroy the poles and floors , the nest will stay floating and spawning , in my case just stops when they are 3 or 4 graydwarfs