stereo mode in webVR, possible to constraint on Landscape mode even if rotation with device ?

Hi,

so here my problem :
-when enter WebVR with stereo mode,
if orientation of device is landcape : the screen is split from the longer part of the mobile (giving 2 squares),
but
if you rotate to portrait mode : the stereo view rotate and screen is split from the narrower part of mobile (giving 2 long rectangles)

is it possible to keep the landscape stereo mode (2 squares) when rotating in portrait mode ? (same as youtube behavior)
(i assume stereo mode keep the same but image rotate)

i was thinking of an action in Onresize Event triggered by orientation change,
comparing stagewidth and stageheight and resetting stereo mode placement...

thanks for help

z