Some of my mnemonics worked so well for me that I am no longer getting those characters to practice. Is it possible to add those mnemonics somehow, such as through the vocab viewer perhaps?
Rachael.

You can use the scratchpad.

We're working on a new word pop up that will be accessible throughout the site, from lists and the practice page and anywhere else you have access to words, and you'll be able to view and edit mnemonics from there, among other things. It'll sort of be a combination of the lookup box on the practice page and the word page you go to when you click a word in a list or the viewer, and will replace both of those with additional features neither of them have.

Until then, yep the scratchpad is probably your best bet.