I used 14x part 3307, 1x6x2 arch piece to make the hole, and 4x part 85080 to make each hollow stud (part 87081 could be used to make solid studs). Due to the lack of a 1x6x2 inverted arch piece, I had to make the bottom half of the brick studs-down, and I used tiles to smooth the bottom. This brick will not stack as real Lego would.
I'd really prefer to build this in orange, but Lego never made 2x2 quarter circle bricks in that color, so I had to settle for yellow.
Here's an exploded view showing how I centered each 4x4 stud in a 7x7 area: