Lately, I've had to cover an area at my job that requires me to stay behind a desk. Fortunately, there is a storage area immediately behind it that I often slip into, at least to stretch. Anywho, that's a pretty good list of things you can do at work. Some more discreet than others.
You may also have to be the "kooky health person" and be conspicuous now and again. Any one who jokes about it will only be doing so because they feel bad about being less health conscious.