In theory I can see how it works.
If you take a piece of tissue paper and wet it, you can form it into any shape you want. Once it dries, it will stay in that shape. Think the same way about playing cards, if the cards get wet, they temporarily lose their snap and get softer, that means you'll be able to bend them as you wish, without them resisting.
It seems to work differently for different people though. One person told me to put the cards inside a ziplock bag in the freezer, and that sort of cancels out my theory. One said something about a vegetable-crisper. I tried it once myself and I didn't really see any effect personally.
The best thing to do would be to make the deck humid somehow, put it in the box in a card clip or under some heavy books or something, and leave it down there until it's dry. The cards might hold onto each other a bit on the edges, but you'll quickly get them separated again if you play a bit with them.