I don't use rockwool so I can't answer specifics about it, but if you rooted them in rooters or something you can just transfer that directly to your net pot and fill carefully with hydroton.

Now the key is, putting them under the MH its gonna get very hot so you should actually raise the water level up enough so that the bottom of the rooter is actually in the water. Within a week when the clones have grown a bit and furthered their roots, then you can drop the water level down to below the net pot level.