Kicking the boxes with the animation is very easy, just make 2 boxes, stick them to the foot and knee bones and the rest is done from the animation. (If you use physx)
The bone adjustment on different heights should be a bit harder though, you need to get the ground rotation with hit.nx & vec_to_angle, then you have to write a function which adjusts the bones to every given angle, so you have to make some formulas.