Splenda is perfect for sweetening soda. You can then either force carb in keg (my choice, the absolute best way IMO) or go ahead and bottle condition. You would need to mix a yeast slurry in of course and some yeast nutrient. The carbonation process would eat up the sugars to an extreme degree and the product should be fine for a diabetic... As noted above, Splenda will not ferment. When the product came out, I emailed them for this very reason. I never actually made the soda, but the above info is what they sent back to me. Good luck and let us know how it turns out!