I have a very simple reversing trolley O scale layout and I am trying to figure out how to automate it.  It is essentially a Y with bumpers on all 3 ends and uses a fastrack switch to choose direction at the Y split.

Is there some way to use the Non-Derailing Function to automatically have the switch change the direction when the trolley isn't in contact with the switch itself? 
Ideally, each time the trolley hits the bottom of the Y (or makes contact with some portion of that track below the split) I want to signal the switch to reverse itself.
That way if it came from the left branch on the way down, it would go up the right side on the return.
And back and forth...

It feels like it should be possible, but I'm not electro-savvy enough to figure it out.

Any help would be greatly appreciated!