Here is the basic process:
Invert image along the Y-axis or render shadow type image which will be more accurate
If inverted then probably some manual painting is required to mimic the reflection shape
In Photoshop I used gaussian blur with 5 pixels radius

So how this works. In image Red is ...

Hey, did your request. It sounded interesting to make, here are some graphics which somewhat fits in the world, works with gates and other entities which interacts with the walls. Also added lua file with correct shiftings which you can use.