in 5 days you will come back to crispy critters, all you gotta do is hook a timer up to a water pump that will draw water from a basin and flood the cubes 2 times a day. Must find a way to water the plants, heck you can use buckets of water with string hanging into the water and up into the roots to keep em watered if you had too. The strings will wick the water up them to the plants. Maybe you could setup a drip system?
Have anymore rockwool? soak the hell out of a bunch of them and place them in a tub of shallow water, place your cubes on top of the wet ones.
These are just some ideas. I once went away for 4 days and my water pump had broken, came back to 3 surviving plants out of 20, so I know what is going to happen.