You can add subClippboards under any Clippboard. To do so, mouse over your Clippboard in the menu on the left, then click the + that appears next to the Clippboard. Just name the new subClippboard, and it will appear alphabetically under the top level Clippboard with any other subClippboards. Click the arrow next to the top level Clippboard name to collapse and expand the subClippboards in the menu.
Watch a video about Clippboards and subClippboards.