If you only want to play the game, all the USBLoaders can dump your game to the expected format to play it from SD or USB. Launch the loader of your choice (CFG Loader, Wiiflow or USBLoaderGX) and insert the disc. look for the dump or install menu.
The game will be dumped as a "wbfs" file format, which contains only the game's data and will be smaller than the real disc size.
If you really want the "ISO" format, then you'll have to use CleanRIP, and it will generate a full disc dump (4.7GB for single layered games, 9GB for dual layers).