You know a few things from the very beginning:
Your top laner will inevitably shove him into tower; whether it be by an eventual slow push after they've frozen some waves against him, or whether nasus has managed to break a freeze and has gotten a wave to push back to him.
You know their jungler will likely live top regardless. Nasus is great for setting up ganks. No CC skill-shots required. Nothing, he just tags them with wither and its an easy kill.
You know you have the advantage in top lane early, so you can make plays on their jungler. Nasus cannot abandon farm early, and if he does he's not very strong in 2v2s. Generally the team with Nasus in 2v2's almost always loses.
In short, **Nasus lanes are generally lanes won and lost by the junglers.** You can hate that, it's fine. But some lanes are like that. Some champions draw that much attention to their lanes. It is incredibly important, that you be there for your top laner. If it is very clear Nasus' jungler has abandoned him for whatever reason, even better: he's incredibly easy to dive even at early levels.
But what happens? Time and time again, junglers leave their top laners to be camped to death by the enemy jungler and then the junglers lash out at the top laner. You have to understand the circumstance of a top laner against nasus - and trust me, I'm a Nasus main so I know this to be fact: your top laner will eventually push against nasus. It is GOING to happen. Setting up a perfect freeze is actually very hard against Nasus, because he can use his E to shove your wave in and bully you off a freeze with minion advantages early - that's the one thing he can do against most champions not named Kled, Aatrox, or Darius. So Nasus will almost always have a wave shoving to him.
Again, I know you may not like this. But don't think your top laner is just brainlessly shoving in. Nasus players tend to be pretty clever too, and they know how to do things to manipulate a wave into their favor. And often times, you're stuck with a decision as an opponent of Nasus: aggro and keep him off as much CS so when the wave crashes into his tower, he misses some and can't sustain as much or let him free farm. What do you think the decision will be? It's easy.
So again, junglers, do not abandon your top laner in a Nasus lane. It is the easiest lane to win because you know where their jungler is going to focus his time around. And if he doesn't, it's free dives all day. Win-win.