This is really simple to do because the line trace gives you all the information you need. The hit result will contain something called the impact normal. This is the direction the hit surface is facing.
All you need to do is take the impact normal vector and multiply it by a negative number (opposite of the surface direction) that you feed into an add impulse node. You can do this off of tick or a timer if you need it to be consistently added.
Make sure to check velocity change on the add impulse node to factor in the mass of the target.