Can you elaborate more of the SSD’s being non-repairable? They look at a glance like regular m.2 drives, albeit with some kind of custom housing.
If the only issue is support for the T2 chip, you can disable boot restrictions by starting in recovery mode and using the Startup Security tool from utilities, which allows booting from external drives, so maybe this would do the same for non-Apple SSD modules?
Might be worth noting that the white squares on the board are tape also; I didn’t realise this until I struggled with a later step, so you’ll need to carefully peel these pieces of white tape back before continuing.