All he has to do, and probably worked on, is defending against the left hand. He's done this with bringing in smaller, top shelf boxers to emulate Conor's quickness and angles. Conor has done the same with larger boxers. The difference is, Nate saw pretty much the full arsenal/barrage of boxing that Conor has to work with under a 10 days notice. He will be able to come into the fight sharp from a ton of sparring rounds to mitigate some of the shots delivered with Conor's fast, powerful left hand.
The difference in this fight, IMO, is that Conor showed Nate most of his playing cards but, before he got a taste of Nate's suffocating boxing pressure, he panic-wrestled. Conor didn't truly experience/weather much of Nate's boxing enough to understand how the Diaz brother's boxing is effective. So without undergoing that style of pressure, I don't know that Conor is fully prepared. A well prepared Nate should make the 1st round of this fight look like the 2nd round of the last fight. Conor is a badass fighter/finisher, but he has finally met, in the beautiful words of Pantera, "an immovable stone in your world of weak".