how to get 4x4 rock cubes into ebb and grow buckets

I have a few plants from seed in 4x4 rock wool cubes that are about 8" tall . They are in a flood and drain 2x4 basin. I want to transplant them into a 3 gal bucket ebb and grow system, with clay pellets, when they reach about 18" high for flowering. Two questions.
1. What should I do if the roots start poking out from the bottom before they reach my transplant height?
2. When it does get to be transplant time how should I place them in the ebb and grow buckets?(clay pellets) thanks for any help you can provide.........

Just take off the white plastic around the cubes and bury them in the pellets in the net pot. Simple, the roots grow out into the clay pebbles..