Here is what I did:
SystemMenu 3.3Uv1 (so IOS30 is trucha patched).
No previous IOS16 on the system.
I obtained IOS16 v512 using NUS Downloader v1.1 and packed it into a WAD. Installed that:
Title=1-10 (IOS16) vers: 2.0 (512)
Using Sorg's modified WAD Manager 1.4 I attempted to install IOS16 v257 using IOS30 and got an error (-1035).
Using Nicksasa's FSToolbox I dumped the TMD from 0000000100000010 to my SD card.
Using a hex editor I changed the value at 0x1DC in the TMD to x0001.
With FSToolbox I wrote the modified TMD to the NAND:
Title=1-10 (IOS16) vers: 0.1 (1)
Using Sorg's modified WAD Manager 1.4 I attempted to install IOS16 v257 using IOS30. Success:
Title=1-10 (IOS16) vers: 1.1 (257)
This means I was able to successfully install IOS16 v257 on a system that already had IOS16 v512 using a trucha patched IOS.
I have no idea if this would work on a virgin 4.0 Wii, but it may be worth a try. Also since the LU64+ Wii's don't seem to have any trouble using IOS16 v257 this may be a way to install cIOS 4.0 systems without using the DVDX installer.
SystemMenu 3.3Uv1 (so IOS30 is trucha patched).
No previous IOS16 on the system.
I obtained IOS16 v512 using NUS Downloader v1.1 and packed it into a WAD. Installed that:
Title=1-10 (IOS16) vers: 2.0 (512)
Using Sorg's modified WAD Manager 1.4 I attempted to install IOS16 v257 using IOS30 and got an error (-1035).
Using Nicksasa's FSToolbox I dumped the TMD from 0000000100000010 to my SD card.
Using a hex editor I changed the value at 0x1DC in the TMD to x0001.
With FSToolbox I wrote the modified TMD to the NAND:
Title=1-10 (IOS16) vers: 0.1 (1)
Using Sorg's modified WAD Manager 1.4 I attempted to install IOS16 v257 using IOS30. Success:
Title=1-10 (IOS16) vers: 1.1 (257)
This means I was able to successfully install IOS16 v257 on a system that already had IOS16 v512 using a trucha patched IOS.
I have no idea if this would work on a virgin 4.0 Wii, but it may be worth a try. Also since the LU64+ Wii's don't seem to have any trouble using IOS16 v257 this may be a way to install cIOS 4.0 systems without using the DVDX installer.