[fragmede]

It's hard to know, as you don't mention what physical USB device you're trying to circumvent, but virtualization has come a long way, especially if you take advantage of PCI pass-through. One approach, then, is to run Linux as the host OS, fake the USB device on Linux (hell, the Linux kernel has USB/IP support), and pass that into a virtualized Windows instance, which will just see a regular USB device.

[corndoge]

This is an option I hadn't thought of, but the typical end user won't want to do this or know how as it's a gaming peripheral. I can't be more specific as there are some legal barriers I'm sorting out right now.

[ZirconiumX]

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

[fragmede]

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.

[corndoge]

Because the software controller uses Windows system calls (SetupAPI & DeviceIoControl()) and not DirectInput. Can't do it in hardware for the reasons I mentioned in the op.