I'm sorry to hear about your injury. I hope your knee gets better soon! But you have a great attitude about trying to do other kinds of workouts as you wait for your leg to heal.
When I have had similar problems in the past (e.g., stress fracture in 2010, hamstring trouble this year), I have taken it as a sign that I should focus on my strength training, and I have made some real progress on developing some good habits around upper body and core strength.
Also, do you have access to a pool? If so, you could swim just using your upper body - wrap your legs around a "noodle" and then do breast stroke or front crawl.