Good link to help you get through this:

http://www.ineedcoffee.com/03/coffeediet/

When you check out what Starbucks gives you in one of those creations-you realize you might as well go next door to Hagen Dazs !!

Also - you can heat up the Atkins chocolate shake mix. I tried the soy milk/sugar free chocolate syprup combo and it didnt taste anything like what I wanted.
Cocoa has no sugar, if you can get water and cream and splenda together with it you could safely make something similar to what you want.