1 tsp sugar = 4g carbs - you could probably do fine with that if you wanted to try it on for size. It's not exactly TNT perfect but it's probably in range. it's the unflavored part that would get me with the whey.
I've used flavorings from
LorAnn with shakes for a long time - they aren't sweetened - In the past I used them with a vanilla (and sweetened) protein powder - but they also go well in my unflavored unsweetened whey if I use a little sweetener with it (I use liquid splenda but again - you might be fine with actual sugar).
I tried making up some of my unflavored unsweetened whey when I got it - worse than tasting formula -