I take the train home, which makes it much easier.
When I take the train to work, door-to-door is about 35-40 minutes, so I'm getting an hour plus of exercise, and only adding about 30 minutes to my commute, kind of a 2 for 1. Unfortunately, road biking is pretty efficient, so it's not like it makes me super fit. :-/
I used to do this all the time, but the teen parenting years were hard on me and my exercise routine. It's something I've returned to now that the kids are both in college.