I'm not sure if you really can. I play Nasus quite a bit and I've always regarded Irelia as a free lane since she is:
- attack speed reliant (Wither cripples her damage)
- melee (can't harass you under tower easily)
- weak early game (so by the time she has the damage to threaten you, you are already tanky and have stacks for sustain)
All I can really recommend is to have a strong early game jungler and call them to gank your lane early. You should be sure to avoid pushing the minion wave under Nasus' tower so that you can still harass him and leave him vulnerable to ganks (while protecting yourself).
If you get counterpicked by Nasus, it might be a good idea to swap with your bottom lane so they can bully him away from CS. You will be denied as well, but Bladesurge can help you last hit under tower and you will be prepared for it.
Worst comes to worse, hope someone on your team is capable of kiting Nasus out during teamfights while you focus on assassinating the enemy backline.