I got really excited by your idea of using the keyboard shelf for my machine. I don't know why I never thought of trying this before. I have these computer tables in my workroom that I bought years ago from Sams Club, I think. They are shaped in a wide U, with the pullout shelf in the center of the U. The shelf seemed sturdy enough, and when I tried my machine on it today, the small extension table I have for my Bernina 1090, which is about 6x12 inches, was perfectly even with the surface of my table!
I am trying to teach myself to free-motion quilt and had been looking at a much bigger extension table, but this might work just fine. My body has to get used to the much lowered position though. I felt really awkward, sitting that far above my machine. I lowered my chair, but then I felt too big for the chair. Weird that.
The other problem was that even though I had all that even space around my machine, the small quilt sandwich I was attempting to quilt wasn't sliding around as freely as it did when the machine was above the surface. I think this must be a posture problem, in that my hands aren't putting the proper pressure where they should be. When I put the machine back to its normal place, the sticking problem solved itself. Time to practice more.
Thanks for the suggestion!