Sending a keystroke to a USB device

[brutforzzz]

I have a USB device plugged between a PC and a USB keyboard. The device normally works by responding to keystrokes from the keyboard, but what I want to do is to generate keystrokes programmatically from the PC. I know that OUT is an "unnatural" direction for keystrokes, but I hope to activate the device that way rather than by user interaction.

Note that this is completely different from internal Windows events such as KEY_UP/DOWN/SendInput/etc. Does anyone know how to send a keystroke?