I've done it, and there's a slight problem because the co2 changes the flavour of the wine and it took an innocuous white into something that tasted like the vilest of trampagnes, sort of Special Brew territory. I also did a red and can't remember what it was like. I think the same thing, basically it needed to be sweeter. If you've tried Banrock Station Sparkling Shiraz the morning after a party it's really quite sickly (but needs must).
So, I'd start with a little tester of wine you already have, carbonate a bit - I use a pop bottle and carbonation cap I made from the schrader valve - then use some stevia or something to find a balance. Don't throw it in as powder.
