Basically as others have said, the only way to get 100 shots is to shoot ONLY JPEG (Not RAW + JPEG). (edit: and only use the CF card to write to) My D300s will happily go to 100 shots on the internal battery (albeit at a "limited" 7fps) With the MB D10 and AA batts it, in theory, will go to 8fps, but the difference in frame rate is hardly enough for me to worry about - for you it might be the difference of getting "the" shot or not.
edit: Having now conducted some experiments, it seems that the "speed" of the card in the camera has a lot of bearing on its ability to reach the 100 figure. With a 200x CF and a class 10 SD card "JPEG normal large" image setting it only got to 28 images. Remove the SD card - goes to 50 images Change the 200x CF for 600x CF with class 10 SD - 28 images remove SD card (ie fast CF only in camera) 100 images and write light goes out almost immediately. This with the camerqa set to write to both cards at once, so if the setup was changed to say "2nd card as overflow" things might be different. The limiting factor would therefore seem to be how fast the card can clear the buffer, within the limit of the write capability of the camera (approx 30Mb/s).