Jabberwoku (https://www.thingiverse.com/thing:2291400) recently posted a toothbrush holder for a SimpleHuman bath caddy that was similar to what I needed, except I wanted fully closed circles on the holder platform rather than just smaller open circles.
I remixed and modified a design posted by nick_tc at https://www.tinkercad.com/search?q=simplehuman to make generic front and back blanks that affix to the SimpleHuman bath caddy by use of a single #4 screw.
Now it is a simple matter to make the specific holder protrusion you wish. Use the design software of your choice to make the protruding element that you desire, then merge that creation onto the front side of the generic blank. Use the provided generic back blank to mount your creation onto the caddy frame.