I also work in government - lots of desk work! I found the Virtual Treadmill and that has helped me get some exercise. Basically, I set my laptop on an empty cardboard box so that it is up higher, and I march in place while I type. Right now I am transcribing so my concentration doesn't have to be that high, but I find the marching is easy to keep up. I do it maybe 15 or 20 minutes at a time, but it's supposed to be equivalent to walking 3 miles an hour.