[Gear VR] blob shadows using decal or ... ?

So I asked this question at UE4 forums: https://forums.unrealengine.com/showthr ... w&p=484028

and got a hint that simple blob shadow can be done using either decals or "Worldpos behind translucency". Sure enough no links to training materials about "Worldpos behind translucency".

Can someone please explain how to set that up ? Thanks