Wow, love the usage of non-conventional input! 
It should be possible to just add a new gamepad entry, as you said.
Copy the default.gamepads from builtins to your own project, then change the gamepads entry in your game.project to point to your new file:
But since the controller identifies as something not available in the current default.gamepads file, you will need to add an entry for it yourself. Thankfully we have a little tool for this, hold on and I’ll upload it here, what platform are you running on?