Well, it has been ages but I wanted to post an update to this thread. Ultimately, my resolution to this problem was to lie to everything under all circumstances and hack my way through it. I could have thrown some money at this problem but I opted to throw time at it instead.
The $ version of this resolution would have been to buy a face grooving tool similar to Face Grooving Products or use a lolipop cutter and cut this top on the mill.
The video below will give a detailed account of how I approach this, as presented (live) to my local MakerSpace. Since this video was posted I did add some FOR loops to the gcode program in order to automate the automatic advance of this tool path. I will post that when I have a minute to gather my notes on that edit.
Solution
I started with one of our button insert lathe tools (SRDCN 06-2J) and then hand ground in some relief.
Then I lied to PathPilot about what I was expecting of it, then tossed half of the generated gcode and had to manually advance the Z axis for each cut.
Feel free to ask me questions.