How about disarming the enemy? It would only work with a one handed weapon. It would be something like this:
You would have to be nearby the person. It would work the same way as vehicle jacking, and you would go into 3rd person. It would be like "Press LB to disarm" and it would switch to 3rd person for the animation.
I know it might not be too balanced but it should only work for people with Heavy weapons such as the Spartan Laser or Rockets.
Thoughts?