9 miles for me and I've never had a problem with wrinkles. I try and get mostly wrinkle-resistant fabrics these days, but still have some items that are prone to wrinkles. For those, I just make sure to fold them nicely and keep them on top of my loosely packed pannier bag. After nearly an hour in the bag by the time I'm putting them on, they're never more wrinkled than they would be after having sat at my desk in them for an hour. Well within our business casual atmosphere at work, especially when you get in an hour before everyone else and they'd never see me crisp even if I drove in! Unlike a backpack, things tend to stay in the layers I pack them in with the panniers.
Also, not sure what gender OP is, but try storing a few cardigans in your office that match most of your outfits. (I keep a grey, a black, and a brown hanging in my office most of the time.) Not only do they keep me warmer, but they are never wrinkled, so can generally hide any wrinkles on the off chance there's a bad fold crease that day.