What is the best USB library to communicate with USB HID devices on Windows?
If libhid works for you, then perhaps the thing to do would be to write an application (which you would GPL), which uses libhid to talk to devices, then provides whatever you need via a TCP connection. Your real application would connect via TCP to do what it needs. This would obviously be a massive performance hit.
This application would effectively be a 'shim' between libhid and your application. In this case, the shim would exist for legal, not technical, reasons.
I'm not saying it's a good idea, just that it's an idea.