Personally, I would skip the rockwool. Get a nice net pot cut a few holes through the net to make them bigger and lightly and gently pull the roots through...I have done this with clones and cut a hole in the center of the net pot and fed the roots through that way. Then fill in the gaps with Hydroton clay pellets.

Hope this helps...

What is the reason for switching over if you don't mind me asking...?