Best bet is blending with a different beer that can compesnate for the issues.
If you would like to ferment the beer further, however, I have heard that if you get a big active cake of active yeast going, and add that to the beer with the sorbate, it will ferment a bit more.
Keep in mind the sorbate will essentially neuter the yeast, so they cannot multiply. So whatever yeast you have going when you sorbate, that is all the yeast you will ever have. As they die off, or go dormant, the fermentation stops.
With a 9% to 10% beer, however, I am not sure how long "new yeast" will go before going to sleep due to the high %.
So if you have a good yeast cake floating around, and the only other alternative is dumping the yeast cake and the beer, give it a go.
Otherwise, if you can, make a thick dry beer, possibly even a low gravity one, and blend the two. That is a much better bet!