You can add synonyms for radicals, kanji, or vocab either on the item’s page or when reviewing it. You can’t add them the first time you see it though - has to be a review. I think there’s a userscript that lets you add them during the lesson.
A warning, though - the site’s mnemonics are all based on their names for the radicals, so you’d have to make up all of your own mnemonics (which would probably stick better with you anyways, but some people like to have the structure already in place). It bugs me a little that WK doesn’t use the traditional radical names for a lot of things, but their versions can be helpful too, especially as they have the related mnemonics in place should you choose to use them.