There are a few ways I've found to make this work:
Option 1: Single standard L-Shaped corner cabinet.
Box Constriction: Framed. Separation: 0".
Delete Door/Drawer to leave single Opening.
The problem with this is that chief leaves a 0" thick surface on the main face of the cabinet that you can't get rid of.
If you can ignore it, GREAT!
Option 2: This looks the best but took 5--yes, five--cabinets. All set to Framed / 0" Separation as well.
Two 12" on the left and right with Right and Left sides respectively, set to None.
Two 3" on the inside of the 12", their noses overlapping, both Left and Right side set to None - this is purely to create the full toe kick.
One 21"x21 in the center, Right or Left set to none, depending on which way it's facing.
Option 3: Same as Option 1, but set the Cabinet material to "Opening (No Material)", Custom Back set to Panel - Inset
Of course this one only really works well if there's cabinets on either side, like in OPs photo.
The big issue with this one though is that the face edge of the bottom separation uses the box material, so it looks like a 0" surface.
To fix this you have to go to the Front/Sides/Back panel, select the Opening, click the Shelves Specify button, set it to Manual, add an additional Shelf, and set it's Spacing From Previous to 0. Which pulls shelf 1 down...
Still probably faster than making 5 weird cabinets that all have to play nice together.
It would sure be nice if they'd add the ability to just remove the stiles.