Replying to a days old thread that will likely go nowhere fast but hey.
As above you might well be launching right into the deep end for this one, finding the location (though that might be as easy as making a new save, backing that up and changing as little as possible do something that gains a friend code to compare with) and possibly dealing with hashing (I don't think the Wii was console wide so you then get to if not figure it out then disable the check so next time round the game sorts it and you can return to stock, or I guess continuing on with the no save hash version).
If it is more I don't want this person on a list then how many are on there? Might be able to play/add/whatever however many games it takes for them to fall off the list. You might be able to push this with an anti ban cheat as well -- most of those will probably alter the apparent mac (the only identifying thing within the console really) so get one of those and cycle it round a few dozen times to hit that limit quicker still (do note though that the wiimfi replacement has some measures to try to prevent this in some people.
Alternative another. You might be able to recreate your existing save on a new save file -- unlocks, inventory contents, play time, records... whatever is likely in memory at some point you can get to and copies that to and from the save each boot which places it in the range of simple cheats.