Gday! What I did was this:
In Wii, simply add the email address that you want to register. then it will send an email to that address asking for confirmation. all they have to do is reply (they dont have to write a message). then its done. it worked for me.
If it doesnt work, ask the other person to send u an email to ur wii email address (which is w1234567812345678 [16-digit wii code])@wii.com. for example my wii email addy is firstname.lastname@example.org