Whenever I've run in place, I've always felt alot more pressure on my knees. I think it's due to a fairly straight up and down motion, versus outdoor running where the force is dissipated as you move forward.
If jumping rope isn't an option, I'd throw together a circuit of burpees, jumping jacks, and shadow boxing. Maybe 10-15 "reps" each done for time, or 30 seconds of each done for time. That should be plenty of work to crank your heart rate and burn some calories.