Sulfites don't stop fermentation- that's why winemakers use them all the time as an antioxidant and preservative for wine. Wine yeast are very tolerant of sulfites (campden, potassium meta-bisulfite, k-meta, etc).
If you want to sweeten a wine, it's really easy. Wait until fermentation is completely done and the wine is clear and no longer dropping lees. Rack onto a solution of 1 campden tablet (crushed) and 1/2 teaspoon of sorbate per gallon (all stirred up and dissolved well). Wait three days, then sweeten the wine to taste.
What I like to do is pull out a sample of the wine and add a simple sugar syrup (or honey or juice or whatever I'm using) to several small samples and taste. If I love it at 1.010, for example, then I'll sweeten the whole batch to that SG. One tip- sweeten to just a bit under where you like it, as it tends to get sweeter tasting in the bottle. So if you like it at 1.010, sweetening it to 1.008 is a good idea.
Then, let it sit two or three days to ensure that fermentation hasn't restarted after all, and then bottle.