I just managed to get 2 jammed batteries out of my apple wireless keyboard-
i mixed a little baking soda with water, as suggested, and using a teaspoon dribbled a bit down onto the batteries.... at first I though it hadn't worked, but then they dislodged pretty easily with a scribe tool about a minute later, whereas before I had been trying to dislodge them like this for ages with no progress at all.
I guess I will have to wait a few days to see if the keyboard actually works once it is dried out though!
Interestingly, it turns out it was an energiser battery that was provided with the keyboard which exploded. (This happened about a year ago, but I've only just felt the determination to do something about it!)
Just before resorting to this method, I gave the technical guys at apple a call, and they seemed to think there was no alternative but to buy a new keyboard!
Also, possibly kind of important:
I read a few blogs just now about removing battery leakage in general, and the general consensus seems to be that these chemicals are not particularly good for you, so it might be sensible to wear gloves and open some windows while you are experimenting!
I'm irrationally hyperparanoid about things like this so just reading this has made my skin crawl slightly, but its probably all in my mind really..