It does not appear to be possible to do the required volume UI in UE4 binary using blueprints.
It is required for any submission to Oculus store. See:
There appears to be something in the Oculus SDK documentation about it such as: https://developer.oculus.com/doc/0.1.0.0-unity/class_o_v_r_volume_control.html#af7b0909826fd67cafef235123860dcc7
I tried creating my own volume UI 3d widget using the assets from the GearVR Mobile SDK however I can’t figure out how to get the current volume. Without knowing the current volume you do not know what value to show in the UI.
Can we get these exposed to the blueprints? Otherwise UE4 is still not supporting the entire GearVR distribution process
Also created a Answerhub question about it: [Gear VR] How to do the required volume UI? - UE4 AnswerHub