Hey Billy,
I think that there are many methods that will work in DWC, what Mr Jorilla suggested will work, I have done it that way, but I have also done a few grow like you have it set up, what I do(taken from SB) is layer the bottom of the net pot with hydroton, then place your rockwool cube on the top, you can gently place pebbles around the cube to give it stability, then as Mr. J pointed out wait until the stem hardens a bit to put the rest of the pebs on top, I also followed SB's recommendations by using some formulex, but I have also used a weak solution of Sensi AB about 1/8th strength.
It comes down to personal choice, either way works well. best of luck on your hydro run!!!