I have done this several times before for this section but I am feeling bored right now:
The command line copy is what you want
This being said you will need to modify the input, the modifier you want is "b"
The copy program/command is remarkably dumb so you are going to have to tell it to do everything including
what files you want to merge and in what order, you do this by stringing the names of the files together with a + symbol
what the file you want to make is called. This comes after the string of files to be merged
The command will ultimately look something like
copy /b 0.bin+1.bin+2.bin+3.bin newwiiiso.iso
If you need a way to get a nice long list of files then dir /b >>a.txt will make a file called a.txt that contains the names of all the files in the directory you run it in.