I found that option, you have to enable a beta feature for that to work, here's how for anyone wondering https://forums.unrealengine.com/showthread.php?530-How-to-enable-Light-Propagation-Volumes-GI-WIP-AND-BETA
In your content browser click on view options in the bottom right, enable show engine content, then copy this asset: MaterialFunction'/Engine/Functions/MaterialLayerFunctions/ML_ExampleMaterialLayer.ML_ExampleMaterialLayer' it can be a good starting point for creating a material layer that has some basic inputs then create…
Wouldn't be surprised if it enabled to render a mesh in one draw call whereas in UDK you would use multiple materials with different ID assigned to different faces.
maybe i misunderstood then, but it seemed like people had found it. https://forums.unrealengine.com/showthread.php?530-How-to-enable-Light-Propagation-Volumes-GI-WIP-AND-BETA