There were thousands of results for my search, but this article from GoodHealth.com was exactly what I was looking for. The exercises could be done sitting down; if I wanted to do jumping jacks and running in place (which was what several other articles recommended), I'd go walk on a treadmill!
The routine had seven steps:
Step One - PUMP. Pump each of your arms overhead five times. Pump both arms overhead five time. Repeat for three sets; this should take about one minute.
Step Two - PUNCH. Punch the air across your body 20 times with each arm. Repeat for two sets, which should take about one minute. (Punching has an added advantage - you can work out frustrations with an imaginary foe!)
Step Three - JOG. Point and flex your toes a few times to limber up your legs then jog in place while seated in your chair. If you need more challenge, lift your knees higher. Use a timer, and jog for two minutes. (Note: This is harder than you think! I started out too fast and had trouble finishing.)
Step Four - BIKE. Lift both feet off the floor and bicycle in place. This works better without shoes, so slip them off if you can. If you need more challenge, lift both knees higher. Use a timer, and bicycle for two minutes. (This one is harder than you'd think, too. I had to pace myself to complete the two minutes).
Step Five - JUMP. Cross your arms across your chest and cross extended legs about calf level. To jump, swing arms outward at the same time as you extend legs outward. Jump back to original position. If you need more challenge, lift your arms above your head. You will get even more challenge if you lift your arms above your head and your feet off the floor. Use a timer. Jump for two minutes.
Steps Six and Seven - REPEAT. Repeat Pump and Punch to cool down.
This routine (which I did two times in succession) definitely got my heart rate up! Since I was by myself, I didn't have to worry about looking funny as I punched at imaginary opponents and jogged in place. However, the cat that was sitting on my desk looked mildly alarmed when I started pumping my arms, and quickly ran away when the punching started.
The only problem I had was my vintage desk chair; it's getting pretty creaky and all the movement made it shake even more. I though it might fall apart, so I moved to a kitchen chair to complete my workout.