| I have the same job. I could easily not leave my desk all day. Things I do:
Deliver notes, memos and so forth in person instead of phone/email
I have to send out a lot of packages etc. We have a runner that we can drop things in a cart and she will wheel it back to shipping every hour or so. I take mine myself
Get up and walk during lunch and breaks.
Now keep in mind none of these things will be a replacement for an exercise program but they will get the blood flowing a few times a day. I would use it this way: Tell yourself "I sit on my ass for 9 hrs a day" "I have no excuse whatsoever to exersice for 30 minutes in the evening." | 
