To Drag Materials onto Sub-Object Selections

In the Modify panel modifier stack, choose Face as the sub-object level.
Select faces of an editable mesh object.
Drag a material’s output socket from the Slate Material Editor active View to the selected faces, or from a sample slot in the traditional interface.
In the modifier stack, click to turn off Sub-Object and return to the object level.
On the Material Editor, click (Pick Material From Object), then use the eyedropper cursor to get the material from the object.
The new Multi/Sub-Object material appears in the active View.