Theoretically this would be possible but probably wouldn't help much in practice. Writes on an SSD aren't mapped 1:1 from "logical" address to physical address - they constantly balance and move writes around the entire device (the "Flash Translation Layer" it's sometimes called). As a result once you have exhausted the normal reserve capacity (perhaps allowing for some early life failures) I suspect it's likely the rest of the device will soon follow and you wouldn't extend it's life by that useful an amount.

I don't have hard data however on like the "curve" of flash cell failures as an SSD ages and therefor exactly how much longer you might get based on the minimum to median cell failure.