Rick, the second pic in the first post should work for you with or without the Mousepad and HD shelf. It would look like the one in post #2 except the clamp would be a vertical mount (Back of your case) instead of a horizontal mount. Two Knob Screws is all it would take to secure it. This would free up the rack spaces in your rack case on the top. The laptop would then sit over the whatever is under it.
Have you ever considered putting a Locking drawer in the empty space in the front? Line it with foam and you can use that to transport your laptop or use it to place Mics accessories. Looks like you have two rack spaces available. Here is my Drawer that I lined with pull out foam. (I have since swapped out the mixer on top).
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Make her a Custom Made Platform! The ones with the rubber sponge that Massages your feet while you stand.