Myself and a friend needed to do something somewhat similar to get an emulation/mocking framework[1] for Corsair Utility Engine. Our hack was to run the Windows driver in a VM, run the framework in Linux, then pass through the virtual USB device to Windows.

[1]: https://github.com/ckb-next/fakeyboard

If it's an input device for Windows games, without revealing the device, why does it have to go through the USB stack? Basically all games on Windows use DirectX, specifically its DirectInput libraries. (It's been a while, so they've probably been renamed, but the point remains that USB isn't necessary for all input devices, though it is up the application as to what it'll take.) Many emulators are more flexible; might take a look there, and if not, there's also Bluetooth - do the fakery in hardware.