It's almost impossible to stop an active fermentation with stabilizers. While it could be possible, what happens is that sorbate doesn't kill yeast but it inhibits reproduction. So, in an active fermention the yeast don't have to reproduce (they've done that already) so adding it might simply stress them and cause off flavors. It would be more likely to work if you could put the wine near freezing, to get the yeast to go dormant, and then rack the wine (still near freezing) off of the lees and hope that there aren't that many still in suspension and add the sorbate. But I'd say it has less than 50% chance of being successful, and the risk of off flavors from stressing the yeast wouldn't be worth it.
What does work well is to wait until the wine is finished and clear. The wine should be racked (siphoned to a new carboy) whenever there are lees 1/4" thick or more, or if there are any lees at all after 60 days. Once the wine is clear, and no longer dropping any lees after at least 60 days in a new carboy, it can be stabilized successfully with sorbate and campden (campden doesn't kill yeast, either, but sorbate works better in the presence of sulfites), and after a few days it can be sweetened to taste. A few days later, it can be bottled.