My used Wee came with a GIVI case and mount, and I did not want to spend money on the adjustable one. I've been out the machining game for almost a decade, but I still have access and a 6 pack of Yuengling still buys a lot of time.
I found a $9 drop of aluminum, and I was on the way. The simple idea was to cut the bolt pattern again but further back and make them slots. I was worried about the length, but I put a 20lb weight on it and kicked it around. The only give was in the actual Givi to plastic plate.
My buddy has a batch of parts leaving to be anodized, and I will send this for free. In the end, I cut a set of slots that I didn't need, so you could have your local machinist make you one, non anodized, for ~$45, and it will last beyond your bike and be solid.
Side note, I fixed those damn bar mounts while I was at it, and I need to zip up the brake light cable. I cut a slot for it, but didn't have it tied up.