I'm not sure if this would count as jumping, but you might want to try it.
1) Squat down in a wide stance (feet shoulder width and a half or wider) with toes pointing forward.
2) Straighten right leg to stand up, whilst bringing left leg up to perform a "front kick". For a front kick, bend knee first, then extend leg with a flexed foot to kick with the heel.
3) Bend left leg at knee, before replacing on floor in wide stance and squat down again.
4) Repeat front kick with right leg, repeat with left ad infinitum 'till you fall on the floor!
We usually do this with our hands protecting our head, so you should be able to do this with your arm in a sling. Hope the instructions are clear.
