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see summary
You have a "Add from palette" context menu on each container node. You can also invoke "Paste" on them (if you copy from elsewhere). To add from pallete only just on "clicking" a container node is not possible. It could be if the gesture was drag&drop which the palette does not support now. But we tentatively plan it for NB 4.2 - then also the Component Inspector could be made drop target.
It is possible if something is selected in the palette.