Almost everyone is trying to find out ways to stay active at work. We've seen everything from jumping jacks on the hour every hour, to offices with treadmills placed right in front of computers.
For some less embarrassing ideas try any or all of the following:
The easiest way to get an extra workout at work: Take the stairs! Everyone should know where the nearest stairs are in your office building anyway, so use them.
Wrist work: Stretch a rubber band using all of your fingers, then over 2 or 3 fingers.
Inner thigh work: Place full water bottle (or anything similar that is not breakable) between your knees and, keeping abs in, squeeze bottle gently. Repeat several times throughout the day.