Look at how Nokia released the n95 NAM model. Its essentially the same size as the original n95 but with BL-6F 1200 mAh which is slighly larger battery instead of the BL-5F 950 mAh.

If Nokia can squeeze the BP-4L into the E71 and n97 (which doesn't hold the stylus) then I'm sure the Nokia engineers could have achieved this.