Exercise with a broken elbow?

Does anyone have any advice or experience with a broken elbow or something similar? It's a minor injury as far as elbows are concerned, so I've just been told to put it in a sling for 6 weeks and not lift or carry anything. I'm not planning on being active until it's much more stable...but when that time comes, does anyone have any suggestions for workouts? Right now I'm thinking stationary bike, and going for walks...I'm planning on doing a half marathon in 12 weeks so I wanna keep my endurance!

Thank you!