After many hours of development (though, in honesty, most of them spent tweaking the starfield background on the ROM selection screen), fn22snesticle.py can now create ISOs containing multiple SNES ROMs. Just provide a directory instead of a filename with the --rom option.
There are some other minor improvements in this release, such as the --literal-buttons and --no-super-punch-out flags. You can read more about them in the README.md file on Github.
The development page will be updated in due time, but for now, just enjoy SNESticle on your Gamecube (in a slightly more convenient way than before!).