One idea for you: How about a stationary bike or just pedals ? Are you able to pedal with your feet ? Even if not, you can get pedals that can be cranked with your arms, so you can get a workout in, that way.

Here's an example of a hand pedal exerciser. You can adjust the resistance on it to set difficulty level.

http://www.amazon.com/Drive-Medical-...edal+exerciser