Slow HMD movement for cinematic capture?

I need to know how to reference the HMD transform so I can smoothly translate (tinterp node) the camera after the HMD. All I can find right now is some external mocap device transform correction nodes. I tried setting up a camera manager and flip-flopping between spawn & destroy and updating the player view, and tinterping, which works just fine without an HMD. Extra smooth camera action. But while wearing HMD, the “lock to HMD” camera setting is ignored after changing the camera so then the HMD movement becomes static. My hope was the character camera would continue to adopt the HMD transform regardless of which camera my view was actually set to.