I've found a method that takes only a couple minutes, but it requires having the custom Plato reader installed. (I'm sure the more popular KOreader might have a similar method)

1. Convert the appropriate "reading states" .json file into .csv using an online converter
2. Remove all columns except for the one with the highlights, using an online csv editor
3. Import into excel, add 2 columns to the right, change titles to "highlight", "title", and "author"
4. Type in the author and title, drag it down until all rows filled

This .csv is now in the correct format to be imported into readwise.

I used to do it a semi-manual way to you (what I did was download the pdf from thekobonotes, use the highlight took in adobe acrobat, then import this pdf into readwise). It isn't that long, maybe 10 minutes, but it feels tedious