How do I pad files?

[TrueDolFan]

I have a working SNES disc that I got from a torrent a LONG time ago, it's the multi-boot rom pack (snes9x plus ROMs). I really want to add a ROM (Terranigma) to it, so I want to copy all the files to my computer, add the ROM I want into the ROM folder, turn it back into an ISO, and re-burn a new disc to use in my Wii. I forgot how to pad it so it will boot. How can I pad the new ISO so my Wii will read the disc?

I tried searching, but I didn't find anything about doing something like this.

Can anyone help?