Use the wedge to find the post for the bed screws, pinch against the bed, then mark a line on the magnetic sheet. Mark from multiple angles to find the intersect.
Use a 2mm drill to free up the screw holes. The screws use 2.5mm allen keys. My ones were inset far enough that they could just spin freely with minimal resistance.
The PEI sheet will just stay flat over the holes, no worries for quality loss.
The author marked this model as their own original creation.