I don't think this would be terribly hard. Just opening up the framework-res.apk files in 7-zip I can find the png files used for the battery indicator, however I don't know the *correct* process to extract and repackage the apk without corrupting it.
Could the battery indicator from the NexTheme be put into a zip file also...i love that battery indicator and it goes great w/ the stock Apex 1.3.1 rom