That's pretty much how you'd do it using the physics behavior. Set gravity to 0 and use linear damping to slow the balls down over time. One complaint I've seen is the collisions can be spongy at times. You can improve that by setting the iterations up higher in the physics settings.
You could use the bullet behavior instead but multiple balls bouncing off each other won't be handled well.
A third way would be to do to custom made physics. This is the very advanced approach, but can yield more precise physics. The ultimate would be to impliment 3D physics for the balls.