@muchado said:

Can one do this in a dynamic component? I wanted to created a "troughed slab" (also known as a "ribbed slab") by repeating a depression across a cuboid, but SU does not make the cut in the surface for the copies.

Sorry, it appears that this has been answered before:
http://forums.sketchucation.com/viewtopic.php?f=289&t=23096
http://forums.sketchucation.com/viewtopic.php?f=289&t=21449
http://forums.sketchucation.com/viewtopic.php?f=289&t=18651
http://forums.sketchucation.com/viewtopic.php?f=289&t=17054

The problem appears to be that SU does not do this. However there appear to be at least one work-around that involves creating the positive volumes and then hiding the lines of the joins. I had thought about joining pieces together, but thought that I would be stuck with the edges, but using the trick of "hiding" the edges solves the problem.