Instructions
Select your desired famous Mii from the famousmii website or a similar site.
Open the "Mii Channel" on your Nintendo Wii. This will take you to the Mii Plaza where you can find any Miis created on this system.
Click "New Mii" and set the initial options for name, gender, height and width. You can change these later to fit the famous person you are attempting to create.
Adjust the eyes, hair, face shape and other attributes based on the instructions provided by the Mii website. For instance, if creating a Gandalf (from "Lord of the Rings") Mii, you would be instructed to select the face shape from row two, column one.