No way that I know of to add USB guitar support to GH2 outside of having access to the source code and adding support the "legit" way. It's certainly possible to load a USB stack as an IRX (loading USBD.IRX and USBKB.IRX to GH2 was how the guy got the keyboard to "work") but there's no known way to make it accept a USB guitar (it would likely power up but that's it).
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