I will be adding half a pound of cacao nibs to my stout here in a few days.
Since the beer will be almost fully fermented at that point is it necessary for me to sanitize the nibs before adding them? If so, can someone please provide me with some advice on how best to do so?
No, just toss them in there. The beer is nearing the end of fermentation and will have a sufficiently inhospitable environment for any contaminants to flourish. The acidity, alcohol, and yeast itself are enough.
Also, keep in mind that anything you do at home is merely sanitization, not true sterilization.
If you wanted to be really safe you could soak it in vodka or moonshine to kill any germs.
For the most part you should be fine though.
Though not relevant in your particular situation, consider also using them in your initial boil. It will both steep the cocoa beans and ensure that they are sanitary. You could steep them in a grain (cloth) bag or just mechanically filter as usual.
