Rockwool Cloning question

My aeroponic system has 4" net pots, and the clones im buying are in 2" rockwool cubes. I wont be using any medium in my pots. and was wondering can i put the 2" cubes right in the pots, or do i have to put the 2" cubes into bigger 4" cubes first. And if that is what i have to do do i wait for the roots to show through the 4" cubes before i put them in the pots.
Thanks,
-Westside

If you put the 2" clones into the 4" pots. what will hold it up when the fan blows on it?

Why not buy some Lava Rock and put the 2" cubes with the rooted clones into the 4" pots surrounded with the Lava Rock? I mean, that's the standard procedure.

Vi