I don't see much of another way .
Could buy submersable pumps the tiny ones for each tray set them in containers of water just enough to use in the tray attatch aquarium tubing or oxygen tubing , hook to a timer that would turn them on after a week the programable ones that could be set to turn the pump off too , would take some expermenting with amounts of water, time to leave running ect.
I did see a plant sitting set up in a catalog .
Gin