How to cast dynamic shadows ignoring Material Opacity?

Hi…

I worked on an “autohide” material to use on top walls of my project:

It works, but I’m not finding a way to make the lights “ignore” the material opacity when it’s 0, if I go behind the wall while the material is with Opacity 1 it’s all OK…

But if I rotate my camera making the walls “autohide”, on move the character the object is ignored:

I’ve tried to switch the CastHiddenShadows, but looks like it just affects the “visibleingame” primitives, is there any way to solve this than not place a game hidden object inside my walls just to cast shadows when the wall vanishes?

Thank you.