What about leaving a fresh set of clothes on a hanger at work in your locker? On the days that you drive into work, you can "stock" your locker with a few days of work clothes.
I'm lucky in that my employer also provides showers and lockers. And, I've planned out the logistics of commuting by bike. But, the shear length of my commute (22 miles), along with my start time (06:30) is a bit discouraging.