I have been working on this idea for a while and watching the posts to see what others were thinking, and finally decided to try it. So thanks to several others who posted there ideas!
I spent all weekend playing in my workshop and came away with a 4 wheel drive Bit powered by 2 motors (2.2's), and 2x 150 mAh NiMh cells. It drives like a tank in that the 2 wheels on each side are driven by a motor and you turn by slowing down/reversing one side or the other.
This required a bit of rewiring the circuit board to use the steering function as a second motor. Once accomplished I scatch built the chassis from sheet ABS (train store materials). I used the stock pinion and secondary gears from a bit and main gears that were larger (stolen from a several dead servos) for the drive wheels. I adapted the wheels and tires from a "Modifier" die cast to give it the looks. It is charged with a 4 cell AA pack but it has tabs on the bottom that line up with the transmitter charger tabs. The body is from a super cheap little friction car I found at a Sav On drug store. It was painted an awful green with purple stickers, I added the roll cage and created the mounts. It now fits any bit chassis.
The little sucker is easily as fast as any of my regular bits and twice as manuverable, it will also climb up and over obstacles far better than the new Wilde char-g's. I wish that Tomy had done it this way themselves!