I used Steve's model https://www.printables.com/model/1016997-prusa-gpio-hackerboard-cover to mount my hacker board to the frame (it's a great model). I removed the “plug” in the cable holder which is normally punched out to connect the MMU cable. Since I don't have an MMU this left a gap from the top into the electronics enclosure and I considered it a risk.
I designed this small “plug” to fill that gap. I printed it using Fiberlogy FiberFlex 40D filament so it is a friction fit. It can be installed from the top with a bit of finger pressure. If you have trouble you could loosen the two screws on the side of the bracket when you insert the plug then tighten them back up.
The author marked this model as their own original creation.