In order to make legally re-distributable ISO images for the Homebrew Channel installer, we had to remove Nintendo’s copyrighted apploader code and replace it with our own; we based ours on the one from GC-Linux. You may find the source and binary for it here:
Here is an empty “template” disc image that you can use in your own projects; it contains the above apploader.
Update: A new version of WiiScrubber is out that I’m told works fine with this template. The old one had trouble detecting it as a Wii disc, as it used the DiscID’s first character which isn’t the more common “R” in this ISO. For future reference, the best way of distinguishing a Wii image from a Gamecube image is probably using the disc magic instead (this is what IOS uses).