I used an acrylic plate, 1in thick.
First - drill four holes into the black Aprilia luggage cover aligned with the holes found in the rack.
Second - cut a piece of acrylic in the shape of that cover. Drill four holes aligned with the Aprilia rack holes. Make sure to countersink the nuts at the top of the acrylic plate. I used s/s hex bolts inserted upside down in the Aprilia rack with 2 s/s washers. They come up through the acrylic plate and I used s/s locking nuts (nylon insert) with s/s washer. It's countersunk and flush with the top of the plate so the Givi rack can be flush on top of that plate.
Third - drill four holes aligned with the Givi rack. The screws will go up and not down since the Givi rack goes on top of the acrylic plate. Make sure to countersink the holes so the conical heads of the screws at bottom of plate are flush. I used epoxy to keep them in place, just fill the holes with it, and push the screws gently in and the excess epoxy comes out the other side, and it sets in minutes.
Fourth - fasten the acrylic plate to the Aprilia rack with s/s hex bolts as described in second, place the Givi rack on top of the plate and fasten to plate screws with s/s bolts
I used a clear acrylic at first but I found out it was too thin so I got a 1in thick piece of white acrylic.
I put some reflective tape around the acrylic plate and it ties in nicely w the rest of the Beo.