InDesign – Prevent background images from shifting when pages are inserted

Hi everyone,
I know the issue has been discussed multiple times and I’ve already searched through existing posts on this topic but haven’t found a clear solution (assuming there is one) or a best practice to follow.
I have a document like in (pic.1), where the images are placed on a “Background” layer and extend to the page bleed.

 
When I insert a single page before these, the result is that the image ends up out of place and has to be manually adjusted (pic.2).

 
What I’d like is a way to make sure the image always stays centered (or even aligned to the bleed would be a suitable option) regardless of whether the page is on the left or right.

As far as I know there's no way to do this using Object Style. I also read this article 
https://creativepro.com/adjust-position-of-objects-when-pages-reflow/

about the AdjustPageItem script, but I only need to move the images, not the text frames, which are already correctly placed.
I’d appreciate advice on the best way to proceed, considering I have no control over where the pages will fall.

Thanks in advance,
Davide