I think it would be hard to find something to do at home that was intensive (ie cardio) that didn't involve jumping (ie some pressure on knees). Are you very overweight? Are you wearing good trainers? Are you carefully following the technique?
Cardio workouts that don't put pressure on knees are cross-trainers and exercise bikes....
I have totally dodgy knees, and suffered a bit in the early days with shred. My tips would be:
1) don't do knee circles - they are so bad if you have knee weakness (lateral strain not great for dodgy knees) 2) Make triply sure that your knees aren't going over your toes, even if it means squatting a bit less 3) star jumps also add a bit of lateral strain - I tend to do one round of star jumps and one of butt kicks or high knees 4) Spend as much as you can bear to on trainers
I have major issues with the star jumps and have found I still get good results by substituting them for one of other less intensive cardio excercises, butt kicks, high knees or even just jogging for the 30 seconds. I would suggest adapting it slightly before you decide to give up on it as I have never achieved such great results from any other workout.