Its a great idea to use the WIZ as a gamepad .. I imagine a scenario where the dedicated controls are all doing the normal USB-gamepad function, and the touchscreen is being used to configure custom controls or provide a virtual keyboard (a la Lebedevs' thingy) .. would be a very nice app to write, imho, and use .. if it worked properly.
What it would take is to get the usb_gadget stuff going already - for gadget_ether, for example, as the first step - and then write a gadget_HID_controller module if one doesn't already exist somewhere.