Actually the documentation says, that you should be able to set the mirror option in the nuitrack.config. And it does as long as I edit the config directly. Unfortunatly it does not do anything, if I try to set it from code. But at least the other hidden option in the DepthSensor does.
nuitrack.Nuitrack.Init ();
//does not work!
//nuitrack.Nuitrack.SetConfigValue(“DepthProvider.Mirror”, “true”);//works great
var sensor = nuitrack.DepthSensor.Create();
sensor.SetMirror(true);