The latest issue of American Quilter Magazine had the instructions but it is very hard to visualize how it works.
You quilt the upper six inches of the front and back in two separate steps before quilting the rest of the quilt. You only quilt the top and its batting and then the back and its batting. You slip the six inch sleeve between the two separately quilted sections. The raw edges of the sleeve will be sewn with the upper edge of the quilt.
Here is the puzzler. "Prepare two extra pieces of binding approximately 7" long. Attach them to the sleeve edges on the back side of the quilt. When binding is added to the quilt, bind the ends of the internal sleeve, carefully working in the ends of the extra binding pieces, to make a neat opening on each end of the sleeve."
It seems that the point at which the ends of the extra binding pieces are worked in is where you would have an awkward bulge and the quilt would not lie flat against the wall. I am not sure how to "work in" the ends of the binding pieces either.
I have been pondering this for hours. I have a feeling your suggestions are better than this one for a two-sided display quilt, but still, a hidden, internal sleeve would be wonderful.