In the past I did something like:(Put into a group so it can be turned off when no longer needed)
spritefalling is the falling boxes - set to bullet speed 0, gravity high (500 ?), bounce off solid ON, set direction ON
spriteground is the ground - set to solid
spritefallin on collision with ground : set spritefalling.bulletspeed to spritefalling.bulletspeed*0.5
and that gave an okish result...