I'd just solder paste and reflow, like a large surface mount device. Challenging to get consistent no doubt, and the alignment would have to be very accurate (o

I'd just solder paste and reflow, like a large surface mount device. Challenging to get consistent no doubt, and the alignment would have to be very accurate (or have a few separate boards), but I think doable. Seems like you could largely automate a workflow for identifying pads in the scan and generating the mirror layout, with simple routing to some kind of standardized interface for the probe lines.