Translucency on Mult-Pass Masks

Hi. I have a quick query.
A lot of the things I do are retail concepts. A lot of these feature a clear acrylic case/tank/box to stop theft. I’m sure you know what I’m talking about.
Sometimes (more often than not) the client would like to see the display on a completely white page.
So, if I do this and set a muti-pass mask it’ll do a solid block alpha channel of the whole unit. Whatever was behind the clear acrylic tank/case in the original render will be shown.
Is there a way of creating a more ‘in depth’ mask that captures the translucency of the material so I can overlay the visual on to any background?
See below for an image of the results I’m getting at the moment - branding and product blurred out because of NDA’s etc…

A workaround I can do at the moment is put a white box right behind the boxes but it’s not ideal!

Hi, it looks like you forgot to attach your image. :smiley:
Without it, it’s very hard to imagine what exactly you are doing and what effect you are after (at least for me).

oh here you go, weird, it was definitely on there…>!
clear boxes.tif (730 KB)

Hi there, perhaps this article might be useful for you?
https://support.chaos.com/hc/en-us/articles/4528490184977-How-to-use-Masks-with-Reflection-Refraction-in-Cinema-4D