Several months back I made this homemade drink holder for one of my other bikes, and it worked out as planned. It was made from a trail/hiking insulated drink holder that I wasn't using, and some spare Ram mount parts that I had laying around. I was going to use this reflector mount bracket that I took off the backside of either my Bonneville or Moto Guzzi when I first got it.

Instead of using it, I decided to try and bolt a 1" Ram ball to one of the bolts on the shroud using a 1" long metal bracket that I drilled and painted black. This way I can move it from bike to bike easily and only have a 1" Ram ball left in place. I've been riding it around for the last week and its held nice and snug with no movement. One of the nice things about the Ram parts is that it allows for some adjustability.