some wiis that were menufactured in mid-2008-ish and after have a higher version of the boot1, so the boot1 flaw that is used to install bootmii in boot2 was patched, and since boot1 is a ROM (afaik) you cant edit, downgrade or replace it.
you will need to buy a new wii that was menufactured before mid-2008 to install bootmii in boot2 and not in an IOS, but dont worry, wiis are dirt cheap nowadays, so you can look for a wii that has the boot1 flaw by their serial numbers right
here, and i wish you the best of luck finding one..!