I remember a time when people would put their tiny plants in a big bottle (about 10 inches in diameter and perhpas 12 inches high) with some earth in it. The bottle is corked and moistures is trapped.
In the same way, you could perhaps simulate a bottle, make a big bag using plastic sheets and make it as airtight as possible. Then you soak the pots for an hour or so before you go.
I have not tried this and you do this at your own risk. Or you could play it safe and contract with a nursery to plant-sit for you.