Thanks for the help, I know I will find myself searching and searching, it seems I may be in a little bit of a pickle to get the right setup. Perhaps a frame mounted chain drive or maybe even start looking at front drive electrics.
Have you bought it yet?
If so, which model, exactly, do you have?
http://shop.soulcruzers.com/
You should be able to fit a 2-stroke in one with the head rotated 180 so the spark plug faces forward with a SickBikeParts jackshaft shift kit but it will be close.
Another option is to make it a center mounted shifting electric so you don't have to mess the wheels, kind of like this fat tire 48V 960W dual disc 7-speed.
Not cheap, but mindlessly easy to operate and maintain other than the awkward 4" wide tires.
If you have not bought a bike yet I urge you to look at 3" wide fat tire bikes.
You get the same cool fat tire look but better performance and not that 'monster truck' feel riding it.
I have build a handful of fat tire bikes and don't like those 4+" tire bikes a bit but absolutely love the 3" ones.
You still can't go direct drive on most anything with a tire wider than 2.125-2.25" wide tires without (in my opinion) really silly measures though so keep that in mind.