Hey guys,
Not sure if your aware but you can edit the previously pain the ass level arc that's used on the title screen (01-40) to work on wii and not just dolphin.
By moving the entrance sprite a few blocks to the right it (I moved it to 20 squares from the edge) it is now customizable!! I have tested on my wii by changing the background and adding stuff like coins, ? boxes, bricks and enemies and had no probs at all, just havent tried changing the tilesets but see no reason why it shouldn't work.
Hope this helps any!