DND and Ring Volume

I need to disable the DND function and also set the ringer volume and prevent it being turned down.

I found I can set the following parameters which work fine

voice.ring_vol = 15
features.dnd.allow = 0

However, the user is still able to turn the volume down to zero (and so ignore the incoming calls)

Is there a way to disable to volume buttons. Or if that's not possible could I send the above config to the phone periodically to override the users setting?

Thanks