So apart from camping his lane 24/7
If that is what you do, then you're making a mistake. You can and should camp nasus early on, with a goal of pushing his lane out and taking the tower (pre-6 dives are a particularly smart idea), but then you leave the lane alone and put pressure on the rest of the map. The top laner should try to get out of this lane at the exact point when Nasus starts being able to win a 1v1 against them, because that is when you can't stop his farming anymore. Then, you gank everyone else on the map and take objectives. Nasus can't respond to this. He can't afford to give up the stacks early on, and even if he does follow he will be an absolutely atrocious teamfighter at that point of the game. Accept that you will lose top tower, and take 2 others and a dragon to make up for it. Use the gold advantage to roll his team. If you aren't far behind, this is relatively easy to accomplish.
if it drags down to late game, you've already lost.
I disagree. A common opinion among a lot of high elo Nasus players is that he doesn't want the game to go too late, because he starts to fall off. They will ask you to group and end before he loses his huge midgame power spike. The reason for this is that in the late game, offensive items start being able to shred defenses very efficiently, meaning that you end up much less relatively tanky in the late game than you were in the midgame. Most tanks do fine with that because they still have CC and initiation and burst to fall back on, but Nasus can't deal with all that damage while he is approaching. In addition, higher access to CDR and CC items in the lategame make kiting him even easier. While he may technically have infinite stacking, it just doesn't matter when compared to what he loses as the game goes on, and he needs the game to go unrealistically long (well past a 6 item build) before he becomes unstoppable again.
So, to boil all that down: if you're losing against a Nasus, try to delay the game. Don't let him take free towers, and try to find a pick on him or his teammates while he's split pushing. He's very likely to overfarm instead of taking objectives, and that can be exploited.
there is little to no counterplay once Nasus has enough farm
Again, I disagree. There is little to no counterplay in a 1v1 when he has enough farm, but there is a ton of counterplay to him in skirmishes and teamfights. His vulnerability to peel doesn't go away just because he has farm. Don't 1v1 him, and you'll have counterplay.