Well, whether or not this is possible, depends on how savy you are with electronics and shaping plastic. It\'s certainly \"possible\" though I would never even TRY to help someone do this because if you did it wrong, the best case scenario is a litle wasted money and likely as not, you\'d fry your Z.
My only advice is this. Yes, it\'s possible, but if you don\'t already know enough about electronics, battery pack building and shaping plastice, your Z is probably not a good place to learn, and you should make it seperate fromthe Z and test it manytimes before trying to modify the Z to use it.
I have seen people take the Z apart and with some wire and a soldering gun, change the order of the battery terminals so a larger capacity 5v battery froma particular motorola phone would work, but the same advice applies there. If you\'re not already adept enough to do it, the Z is\'nt the place to learn unleass you\'r a heck aof a lot wealthier than me.