A friend asked for this and I saw a couple of these on here, but I didn't like the designs for one reason or another. So, I submit for your approval (or not, I don't care) my entry into the battery adapter arena.

You will need three additional pieces of hardware - a 1.5" #6-32 screw with a beveled head (common in the United States for use with electrical sockets and cover plates), a #6-32 nut, and a 1" fender washer with a 7/32" inside diameter hole. The nut is placed inside the adapter and pressed into the recess while the screw goes through the washer from the bottom and is threaded into the nut. Easy peasy.