Hi bwell,
Don't know if there's anything you can do with the bottled stuff...but I'm no expert so one of the senior members can give you better direction on that. For what it's worth, here's how my brother and I backsweetened his apple wine.
Once his wine was cleared he racked it into a clean carboy. We added pot sorbate that we had dissolved in water to the wine to stabilize it. The we mixed up 3 cups of water w/6 cups sugar by warming slightly and stirring until the mixture was clear and all sugar fully dissolved. Then we added this to the carboy in 1/2 cup increments, stirred and tasted until it was where he wanted it. Then he let the wine sit and clear for another week under airlock before he bottled it. When we added the sweetener we noticed a veeerry slight haze to the wine, which solidified his plan to let it rest in the carboy another week.
By doing it this way we assured there was no renewed fermentation and we gave the wine time to clear in the carboy just to be safe.
Like I said, this probably doesn't help much in your situation, but hopefully will be of use in the future....