If you keep the yeast happy, rehydrate it (if you can rehydrate the yeast with Goferm you will create a stronger population) prior to pitching the yeast, you will create a much larger and stronger population, then add yeast nutrient such as Fermaid K split into two or three applications, this will help to keep the yeast from getting stressed and will help to convert the sugars more efficiently.
What type of wine are you making, and which yeast are you using? How much are you making (how many gallons)?
Another possibility would be staggering yeast, you can stagger another yeast addition, in other words, if your hydrometer tells you that the yeast is slowing down to a crawl with a lot of residual sugar left in the must, you can hydrate a few grams (possibly a packet) of a yeast such as EC-1118 to finish the job.
Tom