Hehe, using the cards really is the only reliable way of unwarping them. I've never used a card clip (I guess that when you keep the cards tight for about half a week, they should get straight) and I haven't put a deck of cards in the fridge either if it wasn't for making a special trick deck.
I know that when being in a hot and humid place, keeping the decks cool would be a good idea. However, this is actually to prevent the deck from warping any further due to these conditions, rather than having the cards straight out. As it usually is a manufacturing thingy, putting the cards in a cool place would keep them just the way they are.
Glad you figured it out though!