I would add chocolate malt to my mash tun. Not a high percentage of the grain bill, but not a half pound either, I suppose it depends on your bill though.
I have never directly added cocoa nibs but it sounds fine. I made a tropical stout a few months back. The beer had two pounds chocolate malt, 12% of bill, and it took a minute to mellow out for the chocolate to come through. That beer also had a # of lactose.