I actually came across this:
https://wordpress.org/plugins/advanced-custom-fields-custom-wysiwyg-styles/
Albeit, I have heavily modified it to do some of the things I need it to do for my custom setup, but the basics work and are there to build upon.
Works nicely! I may repost my version into a more generic-use plugin for this, because there are some issues that the author didn’t account for in his code.
Don’t wait around for me though, you’ll probably be best to take that plugin and modify it for yourself too.
