I strongly advise against yeast nutrients, unless you are sure that this addition will not be sensed in finished beer even if yeast will fall to eat it. Once I had a batch less than optimal due to this.
First, you can just stir gently. This may sometimes be all you really need.
Second, more reliable way is to add a packet or three (yes, three, really) of rehydrated dry yeast. With three packets, cell count should be enough to finish big beer even in unfavorable conditions. To be more specific, use pitching calculator. Then multiply by 2, because some cells won't do it in wort already with alcohol. Then use cell count from manufacturer to see how much you need.
Third option is one I prefer. Make a new beer with yeast you need. Small one, about 10-12°Blg. Nutrients, aeration, all that. As soon as you have a slurry, transfer new beer to secondary, and slurry to the stuck beer. That way, your yeast will be fresh, active and accustomed to having alcohol in solution.