Sleeping247 has finally posted all the information we require. Here's a copy of his post, all due credit goes to him, he's a lifesaver!
FOR NTSC-J USERS:
I have a NTSC-J 3.0J Nintendo Wii updated online with the latest version.
I tried the two disk method earlier, and it WORKS FOR NTSC-J OWNERS
There is just ONE thing you must change.
1. Download the game
2. Extract the downloaded files with WinRar into an ISO
3. Make TWO NEW FOLDERS.
4. Copy the original ISO and paste one ISO into EACH of the new folders you have created.
5. Run ONE of the copyed ISOs (leave the original alone...!) with Brick Blocker.
6. Run the OTHER copyed ISO in Region Frii (convert FROM USA to JAP)
7. Now burn TWO discs. ONE with the ISO that was "BrickBlocked" and the second disc with the one that was "Region Friid"
8. Now you have two copies of Metroid Prime 3, right?
9. Try to insert the BRICK BLOCKED game. Black screen. No problem.
10. Insert the Region Friid game. It will now say "Initiating Wii System Update" and you can press "OK". Press OK, then on the next message press "I accept".
11. NOW! Let the update run for SOME SECONDS. Let perhaps 10-15% of the bar get blue, then UNPLUG your wii console!!!!!!
12. Insert the power again, turn on your Wii. You do NOT have double channels now.
13. Insert the game that you Brick Blocked (the one that used to give you a black screen...). Let it load, and BOOM; it works. Now you have a working Metroid Prime game and a non-doubled Wii
I let mine update for Twelve (12) seconds before turning it off.
Interesting! Kinda freaked about yanking the power during the update though... Anyone else try this yet?
I'd give it a go, but I still haven't got the complete ISO yet...