yes, you can do that.
get the forwarder v5.1.dol from here.
inject that dol into a WiiVC channel.
I'm sorry I don't remember if you need to enable or disable the "wiimote passthrough" option to enable Gamepad support while inside the loader. you might have to test and see
Then :
- replace your USBLoaderGX's boot.dol on your SD card with the boot.dol from the 1268mod04 in my signature (yeah, the zip will say 1269mod4 but it's a mistake, it's 1268mod is a 1269 beta
), it allows gamepad support, and fix nintendont settings.
- put your gamecube games on SD card (USB is not possible when using WiiUVC)
the loader will generate a new nintendont setting dynamically for each games.
There is still a bug : HID USB controller seems to be disabled when launched from USBGX in wiivc mode, this is not normal, but I didn't have time to search the reason and fix it.
but, I suppose it's not important, because if you use WiiVC it's because you want the gamepad support, not HID.