I've spent the past 8 weeks spending 40 hours in a cube and an additional 10 hours a week in a subway car. Though, I try to take a walk on my lunch break weather doesn't always make that possible. Did I balloon up on this two month stint? No. I found alternatives to traditional exercise in order to burn calories and keep the weight off.
First, I let my will to live and soul shrivel up. It's funny but we forget that the sould does have some weight and if you can just let the job do it's job you won't have to worry about an overweight soul. It's pretty. For me I just stared at the stacks and stacks of non-sensical filing they assigned me and let the feel of defeat wash over me. Poof! My soul nearly invisible.
Second, I hunted for hairs on my chin and then tried to yank them from my face. Sure it's not running or push-ups or the stairmaster but your fingers and hands sure get a work out. Those little hairs are a lot tougher than they look.
Lastly, I would pick at anything on my body I could find. I usually settled on the piercings in my ears. I pick at those holes until they'd bleed. Rejuvenating damaged skin requires calories to be burned. And, it's never ending fun.