Yes, just make a starter with another yeast and add it. Potassium Sorbate only inhibits the yeast from reproducing. If the yeast (your separate starter, not using the sorbated juice) has already reproduced into a large population of hungry organisms, the sorbate won't affect the fermentation.
If you want to get better answers, ask the question backwards: "Can I use p. sorbate to kill the yeast so I can bottle it before it's done fermenting?" The answer will be a resounding "no".
When making a starter, don't waste your time with honey. Honey is expensive and the ph isn't friendly to yeast. I'm not an expert on starters, I prefer not using them, but in your case, you'll have to. Do more research on making starters. Sugar and juice alone aren't enough to create a healthy big population, but it will work. They need oxygen, nutrients, nitrogen, etc.