well, one way to do it is to test if the mouse is moving.
I gave the paddle an instance Variable MouseLastX. If that isn't equal to the current Mouse.X then you know the mouse has moved, update the instance variable and set the paddle location.
so, if the mouse isn't moving, the paddle wont either... unless you use the arrow keys. Just be careful to not bump the mouse :) You might want to give the player a choice before the game starts though. (I added touch support as well just for fun).