As far as I know, the real-time control options of LBR are both working with methods that we offer new target positions before it actually reach to its previously given target. So the interpolator does not perform exact stop and always moves toward the given renewed target. Thus it's mostly used for tracking things in real-time, with assistance of vision, simulator, control device, sensors or any of such that can give the robot positional information.
If you can feed target positions from the external device(through ROS or tracking devices for a basketball) based on -nearly- real time, using FRI or Servoing(simpler and lower performance version real-time controll; does not require external server program with aid of rtOS, period for accepting new targets is more than aprx. 14ms) is a fine idea for me to think.
The workaround we can think of is to start a movement towards some pose but never use the interpolator commands but use our own interpolation to move the robot to the desired goal. Once we are finished with what we want to do we can drive the robot to the initial goal that iiwa.move(...) wants to reach and stop the robot application.
I'm not sure if I've understood your statement correct, but if you stick to conventional way of commanding motions, the robot will always stop after each motion. Unless you give the whole series of motion commands before starting the motion and make them as one Spline motion or blend them with moveAsync() / setBlending().