Funny I had to do this yesterday and didn't see a way to do it so I did it in cura. Then I saved the separate parts as stl's so I could work on them in simplify 3d. Seems kind of sad that I have to go to free software to do things that paid software should do. I really like simplify 3d for most things but it sure would be nice if they would make it do a few more things like this.
+1 this. Fairly often people share "plates" of parts for convenience, and it's useful to be able to break them apart such as to print parts selectively, or to apply different print profiles to each part.