You can set up a system of tubes hooked up to a timer that bring water to your plants (if you have the money and effort to spare). Otherwise, have you ever tried those aquaglobes? I use them for other houseplants sometimes and I like them, but I've never used them on my girls. Maybe, if you have a few days before you leave you can stick one of those globes in there and test it before you go, to see if it reliably delivers the right amount of water.