Add Solid behaviour to your wall spite - make four and place at each side. Give ball sprite Bullet with 'Bounce off solids' behaviour. Set a starting angle (let's say 40) - done.
I essentially tried the same thing, but the bounce doesn't consistently hit each wall. The bounce either becomes too predictable (pattern never changes) or it doesn't do the sine effect I am after where the ball should hit each wall once, just a different spot each time.
As you can see in my posted JSFiddle, the ball consistently touches each side. With the bounce behaviour and movement set to bullet, the ball could bounce up and down, side to side, corner to corner, but not achieve the sine bounce I am after.
I want there to be somewhat of a pattern in movement, but hit a different point each time. This will allow users of the game to use tactics because the movement will be the same touch each side of the wall once movement, but it will slightly randomise the path roughly every 5 seconds or so.