ST buttstock bag rider ideas other then the OEM?

I doubt it earlier that a ST buttstock can work for me, but another day I ran into a good deal for a second hand, so I got it today.
Turns out exactly as predicted, the problem is that the bottom bracket wall (from bottom face to the hole) is way too thin to hold even a M3 thread. I would like to mount a sled (this same or I can print a new one) to the bottom.

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Let see if anybody made some diy development for it? Give me some ideas :)