Creating Drag and drop of material in shipping version


We would like to create a drag and drop feature in our software. We currently tested physic version (launching ray and check which mesh component is hit), but as we are using generated meshes at runtime we can not rely on a good physic hull for our objects.

The UE4 editor seem to to support drag and drop of material on static meshes, and is able to find which material ID have been pointed. I guess this is not using physic. Do someone know what is the technic behind.
(I start searching into the source code, but any help to find or understand this would be appreciated).