If you must do an automated system the easiest thing to do is set it up exactly like a hydroponic ebb-flow system which you can buy or make easily. Basically put all the plants in a tray, then 1 time per day fill the tray with water using a pump on a timer, and let it drain.
Alternatively turn your lights way down so there is little growth and water use. You could make your HPS run for 3 hours a day and maintain the light cycle with a single 40w CFL. The plants will slow but not die.
One thing that can help is thet "soil moist" stuff. Its that polimer that absorbes a lot of water. Buy that and put a few tablespoons in a 5 gallon bucket of water, wait overnight and the stuff will absorb all the water, then you have this gel that is full of water and you can put a whole lot of that stuff on top of your pots, its kind of like having a slow release of a 1/2 gallon over a week, the main problem is my plants drink much more than that, yours probobly do too.
good luck.
let me know how it goes.