This might work for you in this case. Make the wall out of a one-sided square. Turn it around so the "front" is facing away from the camera. In the preview, the wall will disappear as you turn it.  If you move your camera to the other side, you can continue seeing it while you position and size the wall.

Now go into your render options and enable "Remove backfacing polys". This makes the one-sided square truly one-sided!

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)