This is an article I came across a while back that has a bunch of creative simple ideas, perhaps a few of them will be right for you:
The 25 easy resolutions to transform your health
"Making major lifestyle changes your New Year's resolutions is all well and good - if you manage to stick to them. ... It might be better to think small, as tiny modifications are easier to achieve. And if a healthy action becomes habit, it could last a lifetime. Here are 25 easy resolutions that could keep you fighting fit for years to come..."
This one in particular is really good, I do this a lot (once you get good at it, try one leg at a time):
" Stop using armrests to get out of a chair
This will strengthen your muscles and help protect you against falls in later years. Place your feet firmly on the floor, tighten your stomach muscles, clench your buttocks and ease yourself slowly up to a standing position without using your hands for support.
Each lift equates to a squat - the perfect exercise to tone the major muscles in the thighs and buttocks. Double the effect by also lowering yourself into every chair without using your hands. This is the single most effective muscle-strengthening exercise of all, says Darren Chandler, an orthopaedic therapy consultant. 'It keeps stability in the hips and surrounding muscle.' "
And another good desk exercise prompt idea... make it PM/scraper/TM dings for turkers?
" Do the email stomach crunch
Let the ping of every received email or text be the trigger to tighten your tummy muscles and raise both feet off the floor for a few seconds.
This simple activity works the lower stomach muscles, vital for protecting the back from damage and easing back strain. "
And from the sidebar-ish section at the bottom about willpower... very applicable:
" Another trick [to improve willpower] is to take short and simple exercise. A study performed at the University of Exeter, two years ago, set out to discover what might help people to resist the temptation of fattening foods.
The investigators asked volunteers either to rest for 15 minutes or to spend the time going for a walk. They were then all asked to perform a series of dull but demanding computer tasks. Next to their keyboards was positioned a bowl of chocolates.
At the end of the test, the researchers reported in the journal Appetite that the volunteers who had gone for a walk ate half as much chocolate as those who had simply rested. The researchers believe that light exercise energises people sufficiently to revive their brains' flagging resources and thus bolster their will power. "