This only gets you there if the physical distance between the stereo images on the display is <= the distance between the eyes. If it is greater, you would need to look at something more than infinitely away / behind you (your eyes would have to diverge). In particular if the screen is already quite far away (e.g. a few meters), there's not much more far away you can focus anyway, since there's not much difference in angle between a few meters and infinity.
I have to admit I don't understand your argument, but in my experience:
Stereograms are NOT meant to be enjoyed from across a room.
It's REALLY hard to 'catch' a stereogram from far away, so why are you even trying?
However, the "focusing on-or-through a transparent thing" that WhiteSage mentions works well at slightly further distances and can be used to help you figure this stuff out.
