VR. How to get access to HMD Events when stereo is OFF

Hi to every one!
I’m trying to get switch VR/NonVR mode only by put on or remove HMD from head, but after switching stereo to OFF there is no access to any HMD event enable anymore. I was trying to use “Enable HMD” node and vr.bEnableHMD consol command after switching stereo to off, but “Enable HMD” node also turn stereo to ON. Consol command give no any result. Is there any way to trace HMD events when stereo rendering is turned off?