Marshall, thanks for your recommendation. I did a bit of research on Onshape and taught myself the basics. Someone actually already made something very similar to what you want, and with a couple small bug fixes I released a version that can do pocketing pretty well (I havent tested it completely).
That script can be found here:
https://cad.onshape.com/documents/33...13283b73050449
(Its view only but you can copy and paste it into your onshape platform and edit it if you want)
I am going to continue to learn and experiment with this onshape feature (in comparison to the Thingiverse Customizer), because it looks like that may be somewhat easier to use and also may have more potential for help with designing assemblies, rather than individual parts. Thanks for sharing this tool with me!