See Vovka code:
(vla-SetWindowToPlot
ActiveLayoutObj
(vlax-make-variant (vlax-safearray-fill (vlax-make-safearray vlax-vbDouble '(0 . 1)) (car Window)))
(vlax-make-variant (vlax-safearray-fill (vlax-make-safearray vlax-vbDouble '(0 . 1)) (cadr Window)))
)
(vla-Put-PlotType ActiveLayoutObj acWindow)