just the apply two materials in Maya/max to the different polygons/subobjects and export/import like usual. There'll be two LODslots for materials in Unreal.
I'll use creasing to establish the general form of an object, I'll then convert the smooth mesh proxy to polygons and then continue modeling additional detail from there
You need to reExport the asset, not the material. The material setting in max/maya to physicalize just tells the exporter to take those polygons and 'proxyfi' them.