well you just drawn yourself the answer .. :D
check if the object is in the screen area in that specific spot of the -50 Z and give it elevation based on it( if you don't have the elevation sorted out yet, use scale... is kinda the same thing you make things bigger or smaller based on the position of the logic doesn't have to be real like in a 3d engine as long as it fakes the effect and works).
or wait for the new update where you get the Z elevation expression that was featured in the latest upcoming post.
however you will still need to keep track of the position where the player is at in order to elevate it.