It took me a while to find my routine, but I think I’ve got it set now. Generally, no mnemonics, but I don’t consider it to be rote either.
During radicals lessons: If it looks like a kanji, add synonym. If it is a well-known named radical, add synonym. Else, pick one of the kanji it is present in and add synonym. In all cases, ignore WaniKani mnemonics.
During kanji lessons: Look through vocab words that use it (including dictionary lookup, since WaniKani’s vocab examples can be limited sometimes). If there’s any at all that I recognize, use it to remember the kanji. Otherwise, pick some interesting words and learn those, in order to remember the kanji. In all case, ignore WaniKani mnemonics.
During vocab lessons: not too difficult - learned some of them already in order to remember the kanji, and most of the others can be extrapolated. The hardest part is verbs which always use kun’yomi and are often different than the other on’yomi-using words I’ve used to remember the kanji. Sometimes the mnemonics make sense here.
During reviews: give myself a 10-ish second timer. If I can’t remember, just type some junk to fail it and move on, I’ll remember it better as it’ll come back through SRS more times. I think the speed is also important for staying engaged instead of getting distracted.