Modified 30DS

So I've started and stopped the 30DS on several occasions now. I find that I start when my roommates are gone for holidays because I feel comfortable jumping around and making a lot of noise during the cardio bits, but I feel guilty (being on the middle floor) doing it when they're around.

I know in the first level Jillian recommends doing just the punches for cardio if you have a lower body injury. Has anyone had success doing this? Any other recommendations for relatively stationary cardio exercises?


Thanks!