If I understand you correctly, that is already possible. You can emulate a gamepad axis with vorpX by following the steps below.
Just be aware that this does not work as good as mouse emulation. Gamepad input is filtered quite heavily by most games, so you usually end up with pretty high latency and other issues. I would recommend to do this only if necessary, for example in racing games that do not have mouselook.
1. Press [DEL] to open the in-game menu
2. Go to Input page
3. Set ‘Handle Gamepads Internally’ to Off
4. Set ‘Headtracking as Gamepad’ to Relative or Absolute depending on the game. You should get a grasp of what is better quickly.
If this is done, the head tracker is now a gamepad axis. The final step is to go to the game’s input options and map look left/right/up/down to the ‘Rift-Gamepad-Axis’, exactly as you would do with a real gamepad.