multisport: I also live 4 miles from work and have been commuting on my road bike for several years now. Sunday nights I bring in 4x dress shirts, u/w, socks. I have a suit, another pair or two of dress slacks, and a bunch of ties that I keep at the office. Fortunately, my office has a shower room with lockers. If you're not so lucky, you can hang your clothes on the back of your door or use a file cabinet creatively.

Monday through Thursday I meet my buddy for a 6:30am workout. I go directly to the office from that.

Fridays are usually casual dress here so I ride in khakis and a polo shirt or guayabera. You can buy a fluorescent reflective pants cuff band at the LBS for a couple of bucks. Rubber bands work too. I go slow so I don't get sweaty.

It takes a bit of planning, but after a while it just becomes part of your routine. Then you'll find yourself looking for detours and alternate routes. Pretty soon, you'll be logging hundred mile weeks without even thinking about it.

Try it. You won't be sorry.