I also have a desk job and a long commute each day, but I try to offset that as much as I can by taking frequent breaks and walking a mile or two after lunch--indoors when the weather is bad (we have a skyway at work--don't hate me
). Unfortunately, winters are long here, but when it's warm enough, I head outside for a two-mile walk. I work in a large city, but I'm lucky to work near a lovely paved walking/jogging/biking trail and don't have to dodge any traffic.
That all helps, but I'm not nearly as active as I'd like to be, despite working out for at least an hour 5-6 days a week. On weekends, I participate in events such as water softener salt wrestling and bathtub scrubbing, which helps.