Install the standard countertop.
Export the countertop and load into the Display Part Editor.
Save the countertop as a display object, check the Add to Cutlist and assign a price.
Go back to the custom layout.
Place the new "countertop" as a display object.
You could delete the original countertop, but if you place the display object behind a wall you won't see it or you could hide display objects.
Anyways, the display object does show up in the cost list and the cutlist, but again will not be nested.
After the step of exporting the counter top, you need to load it in the Display Part Editor (DPE) (green and red mug) not the Part Editor. When you save it in the DPE, it offers you an opportunity to assign a price to it and add it to the cut list.