Okay, further report: That Amazon cable works, technically. It’s far too long, it’s a flat ribbon, and neither side has any strain relief so the whole assembly is pretty flimsy and fragile. I used some kapton tape to mask off the exposed pads on the underside of the driver board and attach it to the outside of the lid, and a USB-C extension cable to connect it to the laptop. I’m waiting on a shorter round cable from E-bay (a Thinkpad T480S cable which looks like it’s eDP 40-pin on both sides, with the retaining clip on both sides) and then I’m going to see how much of the lid/bezel I have to dremel away to get the driver board mounted inside.
There are bright/dim buttons on the driver board that work well. I currently have my laptop closed and driving both the driver board directly and a 32" 4k monitor through a Lenovo Thunderbolt dock.
I’d attach pictures, but honestly there’s not much to see other than a patchwork of kapton strips holding the ribbon cable to the back of the lid. The monitor looks and runs exactly like one would expect.