HDRI/Backplate workflow problems

[DIO]

Hi,

I´m still experimenting with the workflow for an interior scene in octane max plugin.
I found a HDRI which has a lighting effect I like. I also put invisible octane light
in front of all windows. You can see the result in the picture "...no_backplate".

Of course I want to have a different view when looking out of the windows than the ocean in the
HDRI in the background. I know I could do this in post using the alpha. But then I would have to
hide the glas and would loose the reflections on the glas from the inside (you don´t see this
on the current quality). So I thought, let´s just make a backplate plane in Octane.
It has a diffuse material with a texture emission map using the background forest which
I cranked up to the amount it looks overexposed.
Usually when I do this in vray I can make the plane unvisible to reflections and to GI.
As I undestand I can´t do this in octane. Is that right?
So of course the reflection in the floor
is a bit different than without the backplate, but I can live with that.
What I can´t live with is, that the entry area of the house on the right is suddenly
so dark? There are weak octane lights in front of the windows there. I have to increase them
to a ridiculous amount to see an effect and it looks wrong.
The only difference between the two renders is the hidden backplate plane. It is too far away
to cast any shadow or affect the GI on the right side of the interior.

Any suggestions?

Cheers