There are some really creative devices called mini exercise bike which are pretty much just pedals on a stand. They fit under a desk and allow for some cardio while seated at the chair. I googled it and found a link for you to take a look. There may be others. At such cheap price, you cannot go wrong.
Just make sure to remind the client to maintain good posture.
You could consider telling your client to take the stairs everyday if that’s an option. I think a good exercise could be just getting up periodically and doing a few body squats, arm circles, a few toe touches. No more than 30 seconds or so if the work schedule is absolutely packed. Getting up every now and then, even for just a few seconds can do wonders for your psychological well-being, in my opinion. You might also tell your client to do some shoulder rolls or some light neck stretches periodically throughout the day (maybe make a figure 8 with the chin to loosen up that neck). Some arm pumps might be useful to get the blood flowing. I really like Karin’s suggestion about the pedals. As far as sitting all day, the best investment your client might could make is something that will offer plenty of lumbar support and cushioning for the seat. Posture can improve with habit of maintaining good posture, so I would be sure to emphasize that. Better posture leads to better breathing, which leads to a better sense of well-being.
Great question! Now that I think about it, MANY people have this type of job. You’ve got me thinking about this issue!
While sitting people can do scapular retractions, pelvic tilts, unilateral shoulder circles, shoulders up and down, adductor squeezes, dorsi-flexion and plantar flexion, ankle circles, wrist circles-flexion and extension of wrist, neck turtle exercises, bicep curls, and a chest exercise where you hold onto the bottom of the chair and pull up. I could go on but you get the picture. Many stretches can also be done in a chair.
Check the internet for inflight exercises.