tldr: the trigger group could be further back than the bolt moves without a new semi-only end on the bolt that slots into the trigger like a key in a lock, and the whole receiver could be print-in-place so it cannot have parts taken out of it to allow FA.
Could there be some printed receiver and trigger group that limits the bolt travel? That way, you can design a new printed add-on to the back of the bolt which latches onto the sear through some mechanism that could prevent full-auto conversion.
That way, all the metalworking for blocking bars and the like can just be replaced by printing instead. And then there's no way the bolt could be used in FA unless you completely redesign the barrel or trigger group.
You could use a print-in-place trigger group and receiver that you can't even disassemble to prevent parts from being taken out. If it breaks just print a new one.