There is a version of the Mocha CFW that supports FAT 32 USB drives, but you need either a full size SD card or micro SD in an adapter to get into the Homebrew Loader to be able to use it. I used it to install larger games so I didn't have to delete anything from my SD card to do so, but since the WiiU menu yells at you if there is more than one USB device (despite having slots for two in the system settings) you can only install the game to NAND this way. But technically you could get by using some old ass dirt cheap SD card, like a 2 or 4 GB one or whatever, and use that to boot into that version of Mocha with USB support.