How to set bReturnPhysicalMaterial on Landscape?

I’m trying to get the Physical Material on a specific point of the Landscape from a Hit Result. But the Physical Material is always returning “None”. According to the tooltip in the Physical Material pin, this is because I need to set the variable bReturnPhysicalMaterial to True to be able to get the Material. Googling [I found how to set this to true on collision components of Actors][1]. But I cannot find how to set that on the Landscape. How do I do that?

http://puu.sh/nU788/644f9abf9b.jpg