Good practice for standing (still) Avatar experience?

We're making a Unity-based surfboard experience and expect the players to be standing and using their hands with Touch controllers to steer in the game.  We want them to see themselves and their hands on the board (via first-person Avatar visualization).  This all works fine with OVRCameraRig and OVRAvatar, with one exception:  Because it's room scale, players can "walk" off their in-game surfboards or otherwise get themselves into odd positions relative to their board.  Disabling position tracking in OVRManager keeps the player camera correctly positioned on their in-game board, but then you lose the Avatar hand tracking.

Any suggestions on ways we can keep the player fixed on the surfboard but still track their hands (without having the hands drift away if the player moves around in their room)?