Convert it to a Morph. You'll then also have the option of assigning separate materials to different surfaces, smoothing edges, etc.
Found time after the lines above to test: Without Morph conversion, you're options in 17 are the same as they've always been for imported objects: you can over-ride the entire object with a single material (screenshot). If 'use object's materials' is checked, than any materials coming from Sketchup (3DS, etc) will be available - presuming that they translated OK. Materials from sketchup come in fine for me... but because of the triangularization and inability to edit, I still think converting to a Morph is a good idea.
