Here is a link to a similar question in the community and to the blog explaining the process in detail.
Attached is the workbook used in these examples. I hope this helps!
Custom Mark Tricks.twbx 305.1 KB
That's an interesting thread thanks for posting! However, I am still having issues getting the multiple shapes to appear. The raw data in the other post is not aggregated, while mine is. This seems silly that this is so difficult to do in this software. This is too easy of a task i guess.