First MII editor for a PC is under development

Enjoy the convenient feeling of total control upon your Mii creation and handle it with ease using familiar tools - a keyboard and a mouse. Create and edit miis, backup and upload them never leaving your windows alone with a help of Mii editor for a PC - it's currently underdevelopment and though the version is 1.1.3 it's state could be described as deep alpha.
But you could grab some readily available miis (like Neo, Borat or Angelina Jolie) and have fun tweaking and customizing them. Or you'd create something completely different for an occasion and impress your friends with newly acquired Wii artist skill.