This is something i wasnt expecting from the demo! When the apprentice is knocked down by an explosion (or an enemy), if you press the jump button he will perform the force repulse move (actually a small one not like the one in the trailer) It happened to me four times the last three days!!! Really cool move :D
Like i said in 2 other places, the best way to do it is to find a volatile container and do Saber Slam.
also, it has no effect on anything, it just looks random :P
Yeah I've seen the small repulse he does when he gets knocked down and jumps back up but I don't think that move even counts as force repulse.