i move plants from soil into rockwool all the time. if i think my soil plant is not performing and needs a new boost, i will wash the soil off the root, wrap the stem in rockwool, then insert it into my dwc. i try to make sure there is enough root to at least touch the nutrient. if i feel the rooting system is not very comprehensive, i will add a sprinkle of rooting hormone to the rockwool.
i don't use hydroton because of the cost and i don't think i would use a dish sponge, just because i would be concerned with what may leach out of the sponge....i am assuming you mean a synthetic sponge? but that raises a good question on natural sponge and i have never considered it but then again, i would image organic sponge is quite expensive. perhaps with you being so close to places like tarpon springs, might be a good experiment.
good luck