OK, you won't do a complete workout in your office. However, adding items such as anchored resistance bands or a pull-up bar in your workspace area can help relieve a sedentary lifestyle by giving you easy access to stretch and exercise breaks throughout the day.
If you don't have a home office you may not be able to make any changes to the physical layout of your cube, but you can keep portable resistance bands, yoga mats, kettleballs and other portable exercise gear in any workspace with a personal storage area. If you don't have even that much space, here are a few simple exercises you can perform anywhere.
Lloyd Kahn's Office Gym [YouTube]