I don't understand your insistence on needing to use USB for direct gamesaving, but a VMC emulator does exist for that purpose, using either IDE HDD or USB drives to store the gamesaves. The problem is that it will fail to work for many games and may cause various undocumented bugs even for the games it does work with.
Personally I prefer using real MCs, with gamesave backup methods to free up space if/when needed.
And if you were just looking for ways to avoid buying any real MC, then you need to think again, because without at least one real MC you can just about forget using any homebrew software at all. Nearly all of it requires MC as the common medium for configuration files.
Best regards: dlanor

