This script is not exactly plug-n-play. You have to mark tiles that you want above the player with a region. Then, you have to surround those tiles with the non-passable region. It sounds complicated, but it really isn't. Check out the demo
Features
Create overhead walls/roofs/ceilings. The player can pass behind them.
Turn the system on and off with a switch.
Using a specific route, define areas where the player can 'pass' through to secret areas. See the demo, in the cave.
Screenies
A map of a mountainous route being setup:
Spoiler
And a house being setup:
Spoiler
Aaaand an in-game, normally you couldn't get where the player is:
Spoiler
Script
Please get the newest version 2.0 script from the demo.