Swiftness Boots
Swifties is a great lane option here. It's cheap, and will allow you to keep distance and maybe even dodge Qs, so you don't get poked to death. Perhaps you can even catch him out with these!
Heartsteel
Heartsteel is great against squishies, and gives tongue range and speed to catch him easier!
Rylai's Crystal Scepter
Okay, I'm not actually sure this one is good, but here's the idea: Alone, Rylai's does nothing for Kench, however, if you build Unending Despair first, and then Rylai's, you're getting good resistance and healing for teamfights with Unending Despair, and the Rylai's will proc off every Unending Despair drain, which will make it easier to catch rats like Kennen too, and make it harder for him to engage. Again, I think this is a bit cheesy, but I've had success with this build in the past, and I think there's a chance it might be viable in this matchup if the rest of the game calls for it. Maybe worth testing?