The problem being? Units getting smoothly knocked back is just a stringing together of lots of unit position settings. You have to know what movement you want exactly, what the parameters are. Then you split it up using usually a constant timer interval.
For example you want the unit being pushed 100 meters in direction alpha (on the x/y-plane) over 5 seconds and that in a linear fashion (constant speed, no acceleration, direct path). You take a periodic timer with maybe 0.03 interval, divide the 5 seconds by this 0.03 to gain the number of intervals, approximately 167 in this case, so there are 167 steps to the target position. Divide the 100 meters by 167, approx. 0.6 meters per step and that's what you add to the unit's current position each interval (0.6 in direction alpha). After 5 seconds (another timer, or you can also count the steps), stop the periodic timer/halt the movement.
If the movement is to be more complex, you will need more maths.