I am not familiar with Wii backup loaders, but I had once to convert an old-plain Gamecube Wind Waker PAL savedata to the NTSC equivalent.
Using an hex editor, I simply replaced the game's code (first 6 bytes) from:
475a 4c50 3031 (GZLP01)
to:
475a 4c45 3031 (GZLE01)
Alternatively, you could...