It's basically the same concept as the Grabber mechanism. The pickup is mounted on a plate that slides in a routed cavity and it is covered by a frame.
Here are some pics of the build process
I cut the parts for the sliding mechanism from the same nine ply centerpiece. I just used the part that was under the neck. I had to remove a lot of wood there anyway.
And I routed some slots for the pickup screws and the pickup wiring
I sawed a hole for the pickup in the part that was going to be the frame. Plus I routed the back side, so the plate with the pickup would fit in nicely.
The pickup is mounted into the sliding plate.
The pickup wire goes through the hole on the side of the centerpiece
This is how the underside of the mechanism looked like in this stage of the build
Had to work a bit on getting a perfect fit for the frame in between the routed gap in the centerpiece
Hope this helps?