Exactly the same way. They just add stats. They didn't change the level of any of the other gear, so it doesn't matter if it's level one or level 99. They just added an arbitrary number after the level to give you a performance gauge. The level at which you can equip it never changed. It's all still 99 just like it always was. That was actually the whole point of Ilevel. So that they could give you a way to gauge the expected performance of an item without them having to raise the level requirement. They can add an Ilevel to an onion rod if they want.
Onion Rod:
DMG 1 Delay 364
Club Skil +5,000 Magic Evasion +120,000
Ilevel: 216,987
I wouldn't. I would make the weapon more powerful. You're the one who said they couldn't do that. You come up with an idea to make those people happy.
PS. What's with all the strike through text? Lern2internetz.