Could you make the ISO Builder work with "Remixed Super Mario Bros Wii"
http://rvlution.net/thread/3645-remixed-super-mario-bros-wii/
and "DarkUmbra SMB Anniversary Edition"
http://rvlution.net/thread/2232-darkumbra-smb-anniversary-edition/
as they both have a full set of new levels in them...