This is actually a technique I use with most things that common sense would tell will sell higher after some patch: I usually start to gather them well before the patch hits and, if their prices are high enough some days before the patch, I sell from 1/4 to 1/2 of them.
This made me some money in lots of situation in which I would normally have lost them. At the beginning of WotLK (when everyone had already reached level 80, but before Ulduar opened up), there was a patch that was rumored to make Dream Shards a lot more valuable. Prices skyrocketed: something like from 4-5g each to 15-16g (I'm not sure about the actual numbers, but it was pretty much like this) until the day of the patch, when in few hours the touch an historical minimum: they had even lost value compared to the prices pre-hype, as lots of players had stockpiled Dream Shards and couldn't find a way to get rid of them.
But since I had sold half of the Dream Shards I had stockpiled just before the patch hit, I actually managed to gain from the circumstances.
What if prices had went even higher after the patch?
I would have lost part of my income, but I would have done lots of money anyway. Selling those mats before the patch made mine investment totally risk-free.
How can I apply this in Cataclysm?
I'm not sure you can, actually. It depends on your server economy.
If there is a lot of people "playing the AH", then there is a good chance that some goods that should increase in value come Cataclysm (maybe the same you're stockpiling... if you're not, you should start to search the net for advices, read blue posts about the expansion and try to figure yourself on what you could do some profit). If prices on some of these items grow higher than when you bought them, just sell some... I usually do this only when prices double from when I took the items (or at least nearly double).