Have you seen the keisei semantic-phonetic composition script? A lot of kanji get their readings from one of their components, so if you learn those patterns, there’s a lot less you have to memorize. It doesn’t apply to all kanji, and for some of them, knowing their composition is less helpful than others, but it’ll still help with many kanji that you encounter, both inside and outside of WK.
Thanks to this script, I have a much easier time with on’yomi readings than I do with kun’yomi readings.