IOS236 installer requires HBC already installed to get AHB access (hardware and memory access to be allowed to edit the RAM where IOS loaded in memory is located)
To install IOS you'll need the IOS Install prevention patch applied (should be done by the Wad manager), but to apply that patch you also need AHB access , so even with the proper IOS58 wad file you'll be stuck. (well, no harm trying! let us know)
Maybe that patch can be applied on other IOS than 58, but you'll need AHB access to patch any loaded IOS anyway.
To get AHB, you need to launch a channel (homebrew channel usually), or you can get it from an exploit which is used by Hackmii installer but was never publicly released.
Do you, by any chance, have any non official channel installed on vWii ? any forwarder? anything which could get you AHB access and you'll be saved!
if not, you can't install one without a signature check patch, which is provided by cIOS or (again) AHB access.